overrides/Gio: Use Platform prefix for platform-only functions

In case a platform-only function is being mapped inside the Gio
namespace and that has a platform-specific prefix, then we should use it
inside the more generic Gio namespace.

This is preserving the pre-girepository-2.0 behavior

Author: 3v1n0

installed-tests/js/testIntrospection.js

@@ -232,6 +232,22 @@ describe('Backwards compatibility for GLib/Gio platform specific GIRs', function
             'Expected deprecation message for Gio.Unix -> GioUnix');
     });
 
+    it('GioUnix functions are looked up in GioUnix, not Gio', function () {
+        if (skip) {
+            pending('GioUnix required for this test');
+            return;
+        }
+
+        GLib.test_expect_message('Cjs', GLib.LogLevelFlags.LEVEL_WARNING,
+            '*Gio.unix_mounts_get*GioUnix.mounts_get*instead*');
+
+        expect(imports.gi.Gio.unix_mounts_get.name).toBe('g_unix_mounts_get');
+
+        GLib.test_assert_expected_messages_internal('Cjs',
+            'testIntrospection.js', 0,
+            'Expected deprecation message for Gio.Unix -> GioUnix');
+    });
+
     it("doesn't print the message if the type isn't resolved directly", function () {
         if (skip) {
             pending('GioUnix required for this test');

modules/core/overrides/Gio.js

@@ -497,13 +497,17 @@ function _init() {
     }
 
     const platformName = `${GioPlatform?.__name__?.slice(3 /* 'Gio'.length */)}`;
+    const platformNameLower = platformName.toLowerCase();
     Object.entries(Object.getOwnPropertyDescriptors(GioPlatform)).forEach(([prop, desc]) => {
         let genericProp = prop;
 
         const originalValue = GioPlatform[prop];
         const gtypeName = originalValue.$gtype?.name;
         if (gtypeName?.startsWith(`G${platformName}`))
             genericProp = `${platformName}${prop}`;
+        else if (originalValue instanceof Function &&
+            originalValue.name.startsWith(`g_${platformNameLower}_`))
+            genericProp = `${platformNameLower}_${prop}`;
 
         if (Object.hasOwn(Gio, genericProp)) {
             console.debug(`Gio already contains property ${genericProp}`);