wp-fractional-scale-v1: new protocol implementation

This implements the WIP wp-surface-scale-v1 protocol, which utilizes wp-viewport for the actual scaling operation.

Todo:

• Figure out the denominator situation
• Replace hack for sending new scale hints from wlr_scene when output scale changes without repositioning
• Send error when a wp_surface_scale_v1 object already exists (apparently we also fail to send an error for wp_viewport)
• Consider having a configurable default scale that can be sent before a surface is mapped. This could be the expected output or the highest scale in the layout.
• Clean up test client
• Real-world test client (foot, imv, mpv?) - got hacky version of foot
• Reconsider name: fractional-scale-v1?

References:

• wayland protocols: wayland/wayland-protocols!143 (merged)
• sway: https://github.com/swaywm/sway/pull/6929
• foot: https://codeberg.org/dnkl/foot/pulls/1006