gtk3: implement GetIndicatorState

(cherry picked from commit 50386403)
(cherry picked from commit 6408b735)

Change-Id: I006c739a9dc876dd9ec83375f76fd1343b39557a
Reviewed-on: https://gerrit.libreoffice.org/20312Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Stahl <mstahl@redhat.com>

vcl/unx/gtk/window/gtksalframe.cxx

@@ -3047,8 +3047,19 @@ KeyIndicatorState GtkSalFrame::GetIndicatorState()
 #if !GTK_CHECK_VERSION(3,0,0)
     return GetGtkSalData()->GetGtkDisplay()->GetIndicatorState();
 #else
-    g_warning ("missing get indicator state");
-    return KeyIndicatorState::NONE;
+    KeyIndicatorState nState = KeyIndicatorState::NONE;
+
+    GdkKeymap *pKeyMap = gdk_keymap_get_for_display(getGdkDisplay());
+
+    if (gdk_keymap_get_caps_lock_state(pKeyMap))
+        nState |= KeyIndicatorState::CAPSLOCK;
+    if (gdk_keymap_get_num_lock_state(pKeyMap))
+        nState |= KeyIndicatorState::NUMLOCK;
+#if GTK_CHECK_VERSION(3,18,0)
+    if (gdk_keymap_get_scroll_lock_state(pKeyMap))
+        nState |= KeyIndicatorState::SCROLLLOCK;
+#endif
+    return nState;
 #endif
 }