Fix Gtk enum property types for older Gtk 3 versions

It appears that older Gtk 3 versions don't accept G_TYPE_ENUM as a valid
GValue type because they consider it to be abstract, so we have to dynamically
fetch the type of each enum with the corresponding 'gtk_my_enum_get_type()'
functions.

Author: stackotter

Sources/Gtk/Generated/AccessibleAutocomplete.swift

@@ -22,7 +22,10 @@ public enum AccessibleAutocomplete: GValueRepresentableEnum {
     /// appears after the caret in the input.
     case both
 
-    /// Converts a Gtk value to its corresponding swift representation.
+    public static var type: GType {
+        gtk_accessible_autocomplete_get_type()
+    }
+
     public init(from gtkEnum: GtkAccessibleAutocomplete) {
         switch gtkEnum {
             case GTK_ACCESSIBLE_AUTOCOMPLETE_NONE:
@@ -38,7 +41,6 @@ public enum AccessibleAutocomplete: GValueRepresentableEnum {
         }
     }
 
-    /// Converts the value to its corresponding Gtk representation.
     public func toGtk() -> GtkAccessibleAutocomplete {
         switch self {
             case .none:

Sources/Gtk/Generated/AccessibleInvalidState.swift

@@ -18,7 +18,10 @@ public enum AccessibleInvalidState: GValueRepresentableEnum {
     /// A spelling error was detected
     case spelling
 
-    /// Converts a Gtk value to its corresponding swift representation.
+    public static var type: GType {
+        gtk_accessible_invalid_state_get_type()
+    }
+
     public init(from gtkEnum: GtkAccessibleInvalidState) {
         switch gtkEnum {
             case GTK_ACCESSIBLE_INVALID_FALSE:
@@ -34,7 +37,6 @@ public enum AccessibleInvalidState: GValueRepresentableEnum {
         }
     }
 
-    /// Converts the value to its corresponding Gtk representation.
     public func toGtk() -> GtkAccessibleInvalidState {
         switch self {
             case .false_:

Sources/Gtk/Generated/AccessibleProperty.swift

@@ -70,7 +70,10 @@ public enum AccessibleProperty: GValueRepresentableEnum {
     /// of aria-valuenow for a range widget. Value type: string
     case valueText
 
-    /// Converts a Gtk value to its corresponding swift representation.
+    public static var type: GType {
+        gtk_accessible_property_get_type()
+    }
+
     public init(from gtkEnum: GtkAccessibleProperty) {
         switch gtkEnum {
             case GTK_ACCESSIBLE_PROPERTY_AUTOCOMPLETE:
@@ -116,7 +119,6 @@ public enum AccessibleProperty: GValueRepresentableEnum {
         }
     }
 
-    /// Converts the value to its corresponding Gtk representation.
     public func toGtk() -> GtkAccessibleProperty {
         switch self {
             case .autocomplete:

Sources/Gtk/Generated/AccessibleRelation.swift

@@ -69,7 +69,10 @@ public enum AccessibleRelation: GValueRepresentableEnum {
     /// set of listitems or treeitems. Value type: integer
     case setSize
 
-    /// Converts a Gtk value to its corresponding swift representation.
+    public static var type: GType {
+        gtk_accessible_relation_get_type()
+    }
+
     public init(from gtkEnum: GtkAccessibleRelation) {
         switch gtkEnum {
             case GTK_ACCESSIBLE_RELATION_ACTIVE_DESCENDANT:
@@ -113,7 +116,6 @@ public enum AccessibleRelation: GValueRepresentableEnum {
         }
     }
 
-    /// Converts the value to its corresponding Gtk representation.
     public func toGtk() -> GtkAccessibleRelation {
         switch self {
             case .activeDescendant:

Sources/Gtk/Generated/AccessibleRole.swift

@@ -188,7 +188,10 @@ public enum AccessibleRole: GValueRepresentableEnum {
     /// Abstract role for windows.
     case window
 
-    /// Converts a Gtk value to its corresponding swift representation.
+    public static var type: GType {
+        gtk_accessible_role_get_type()
+    }
+
     public init(from gtkEnum: GtkAccessibleRole) {
         switch gtkEnum {
             case GTK_ACCESSIBLE_ROLE_ALERT:
@@ -352,7 +355,6 @@ public enum AccessibleRole: GValueRepresentableEnum {
         }
     }
 
-    /// Converts the value to its corresponding Gtk representation.
     public func toGtk() -> GtkAccessibleRole {
         switch self {
             case .alert:

Sources/Gtk/Generated/AccessibleSort.swift

@@ -15,7 +15,10 @@ public enum AccessibleSort: GValueRepresentableEnum {
     /// descending has been applied.
     case other
 
-    /// Converts a Gtk value to its corresponding swift representation.
+    public static var type: GType {
+        gtk_accessible_sort_get_type()
+    }
+
     public init(from gtkEnum: GtkAccessibleSort) {
         switch gtkEnum {
             case GTK_ACCESSIBLE_SORT_NONE:
@@ -31,7 +34,6 @@ public enum AccessibleSort: GValueRepresentableEnum {
         }
     }
 
-    /// Converts the value to its corresponding Gtk representation.
     public func toGtk() -> GtkAccessibleSort {
         switch self {
             case .none:

Sources/Gtk/Generated/AccessibleState.swift

@@ -34,7 +34,10 @@ public enum AccessibleState: GValueRepresentableEnum {
     /// is selected. Value type: boolean or undefined
     case selected
 
-    /// Converts a Gtk value to its corresponding swift representation.
+    public static var type: GType {
+        gtk_accessible_state_get_type()
+    }
+
     public init(from gtkEnum: GtkAccessibleState) {
         switch gtkEnum {
             case GTK_ACCESSIBLE_STATE_BUSY:
@@ -58,7 +61,6 @@ public enum AccessibleState: GValueRepresentableEnum {
         }
     }
 
-    /// Converts the value to its corresponding Gtk representation.
     public func toGtk() -> GtkAccessibleState {
         switch self {
             case .busy:

Sources/Gtk/Generated/AccessibleTristate.swift

@@ -16,7 +16,10 @@ public enum AccessibleTristate: GValueRepresentableEnum {
     /// The state is `mixed`
     case mixed
 
-    /// Converts a Gtk value to its corresponding swift representation.
+    public static var type: GType {
+        gtk_accessible_tristate_get_type()
+    }
+
     public init(from gtkEnum: GtkAccessibleTristate) {
         switch gtkEnum {
             case GTK_ACCESSIBLE_TRISTATE_FALSE:
@@ -30,7 +33,6 @@ public enum AccessibleTristate: GValueRepresentableEnum {
         }
     }
 
-    /// Converts the value to its corresponding Gtk representation.
     public func toGtk() -> GtkAccessibleTristate {
         switch self {
             case .false_:

Sources/Gtk/Generated/Align.swift

@@ -31,7 +31,10 @@ public enum Align: GValueRepresentableEnum {
     /// Align the widget according to the baseline.
     case baseline
 
-    /// Converts a Gtk value to its corresponding swift representation.
+    public static var type: GType {
+        gtk_align_get_type()
+    }
+
     public init(from gtkEnum: GtkAlign) {
         switch gtkEnum {
             case GTK_ALIGN_FILL:
@@ -49,7 +52,6 @@ public enum Align: GValueRepresentableEnum {
         }
     }
 
-    /// Converts the value to its corresponding Gtk representation.
     public func toGtk() -> GtkAlign {
         switch self {
             case .fill:

Sources/Gtk/Generated/ArrowType.swift

@@ -15,7 +15,10 @@ public enum ArrowType: GValueRepresentableEnum {
     /// No arrow.
     case none
 
-    /// Converts a Gtk value to its corresponding swift representation.
+    public static var type: GType {
+        gtk_arrow_type_get_type()
+    }
+
     public init(from gtkEnum: GtkArrowType) {
         switch gtkEnum {
             case GTK_ARROW_UP:
@@ -33,7 +36,6 @@ public enum ArrowType: GValueRepresentableEnum {
         }
     }
 
-    /// Converts the value to its corresponding Gtk representation.
     public func toGtk() -> GtkArrowType {
         switch self {
             case .up: