ui: Don't add our filter function twice
xprop: Don't use GDK for reading text properties
events: Early exit when we get a SN notification event

Nothing else needs to see this.
events: Don't pass any X input events on to Clutter / GTK+
errors: Remove vestigals of old error trap implementation
errors: Kill off meta_error_trap_push_with_return

It isn't special; it's just an alias for meta_error_trap_push.
ui: Kill off meta_ui_accelerator_name

It's unused.
Move meta_ui_parse_accelerator into core/

We're currently using GTK+ for this, but we'll stop doing that fairly
quickly and instead just copy the GTK+ code in-tree.
accel-parse: Copy the code from GTK+ in-tree

We can't use GTK+ for accelerator parsing under Wayland, since we
don't want to go through Xwayland to make that happen.
accel-parse: Integrate Above_Tab parsing code directly into our copy
accel-parse: Add keycode parsing as well
accel-parse: Remove support for <Release>
accel-parse: Switch code to output MetaVirtualModifier directly
accel-parse: Use libxkbcommon for keysym parsing

This kills our dependency on GTK+ / GDK entirely.
accel-parse: Clean up error handling

Now that we have the code in-tree, we can change the API to actually
report an error rather than checking afterwards.