ZWidget Wayland backend improvements (Part 1)

[LupertEverett]

Known bugs from the initial PR is now fixed. Now you can run SurrealEditor and the launcher window disappears once you start the game/editor.

Alongside that:

• Menus are now working (a bit buggy though).
• Open file dialog is now working.
• Implemented key repeat functionality using a custom made timer class. This new timer can be used by other backends as well.

Menu bugs:

• They're not being positioned properly
• Switching between menus can crash the app sometimes
• They don't stay open when you stop clicking
• Their states don't match with the mouse pointer's position (wrong item gets highlighted)