Implemented "Open explorer" contextual menu.

Opens file manager for correspondidng directory.
Added to the project and files views.

For eng/ide/gnatstudio#530
Depends-On:https://gitlab.adacore-it.com/eng/ide/gnatstudio-internal/-/merge_requests/194

Author: ogorodnik

share/plug-ins/explorer.py

@@ -0,0 +1,53 @@
+"""Contextual menu for Explorer
+
+This script provides a contextual menu for
+file or directory to open
+explorer in this directory.
+
+"""
+
+import os
+import GPS
+import os_utils
+from gs_utils import interactive
+import subprocess
+
+
+def can_execute(context):
+    """A filter to only allow this action for project or files view"""
+    return (
+            context.file() is not None or context.directory() is not None
+    ) and context.module_name in ["Files_View", "Project_Explorer_Project"]
+
+
+@interactive(
+    name="Locate in Explorer",
+    contextual="Open explorer",
+    filter=can_execute
+)
+def on_activate():
+    gps = os.environ.copy()
+    sys = os.environ.copy()
+    for k in gps.keys():
+        if k.startswith("GPS_STARTUP_"):
+            if gps[k] != "_ABSENT_VARIABLE_":
+                sys[k[12:]] = gps[k]
+
+    path = GPS.current_context().directory()
+
+    if path is None:
+        if GPS.current_context().file() is not None:
+            path = GPS.current_context().file().path
+        else:
+            path = '.'
+
+    if os.name == "nt":
+        e = 'explorer.exe'
+        path = '"' + path + '"'
+    else:
+        e = 'xdg-open'
+
+    try:
+        subprocess.call([e, path], env=sys)
+    except Exception as ex:
+        GPS.Console().write(print (ex))