girepository: Make gi_repository_find_by_gtype() deterministic

When faced with a `GType` which is present in multiple typelibs, the old
implementation was not deterministic, as it iterated over a hash table
of typelibs. The iteration order of a hash table is not deterministic.

Use the new `ordered_typelibs` and `ordered_lazy_typelibs` arrays to
iterate instead, making the order deterministic.

Add a unit test to check this. In particular, to check that symbols
which are present in both `Gio` and `GioUnix` are correctly resolved as
being from `GioUnix`.

Signed-off-by: Philip Withnall <pwithnall@gnome.org>

Helps: #3303

girepository/tests/meson.build

@@ -29,6 +29,11 @@ if enable_gir
     gio_gir,
   ]
 
+  gio_platform_gir_testing_dep = [
+    gio_gir_testing_dep,
+    gio_platform_gir,
+  ]
+
   girepository_gir_testing_dep = [
     gio_gir_testing_dep,
     girepository_gir,
@@ -46,7 +51,8 @@ if enable_gir
       'depends': gobject_gir_testing_dep,
     },
     'repository' : {
-      'depends': gio_gir_testing_dep,
+      'depends': [gio_gir_testing_dep, gio_platform_gir_testing_dep],
+      'dependencies': [libgio_dep],
     },
     'repository-search-paths' : {
       'c_args': '-DGOBJECT_INTROSPECTION_LIBDIR="@0@"'.format(glib_libdir),