ada_api/unparsing: add robustness checks for "group" parsing

Author: pmderodat

testsuite/tests/ada_api/unparsing/invalid_config.adb

@@ -56,6 +56,8 @@ begin
    Check ("invalid_dedent.json");
    Check ("invalid_dedenttoroot.json");
    Check ("invalid_fill.json");
+   Check ("invalid_group.json");
+   Check ("invalid_group2.json");
    Check ("invalid_ifbreak.json");
    Check ("invalid_indent.json");
    Check ("invalid_markasroot.json");

testsuite/tests/ada_api/unparsing/invalid_group.json

@@ -0,0 +1,9 @@
+{
+  "node_configs": {
+    "VarDecl": {
+      "fields": {
+        "f_name": {"kind": "group"}
+      }
+    }
+  }
+}

testsuite/tests/ada_api/unparsing/invalid_group2.json

@@ -0,0 +1,9 @@
+{
+  "node_configs": {
+    "VarDecl": {
+      "fields": {
+        "f_name": {"kind": "group", "document": "recurse", "shouldBreak": 1}
+      }
+    }
+  }
+}

testsuite/tests/ada_api/unparsing/test.out

@@ -56,6 +56,10 @@ a: Int=2
     template for VarDecl.f_name: missing "contents" key for dedentToRoot
 # invalid_fill.json
     template for VarDecl.f_name: missing "document" key for fill
+# invalid_group.json
+    template for VarDecl.f_name: missing "document" key for group
+# invalid_group2.json
+    template for VarDecl.f_name: invalid group shouldBreak: JSON_INT_TYPE
 # invalid_ifbreak.json
     template for VarDecl.f_name: missing "breakContents" key for ifBreak
 # invalid_indent.json