wayland: Implement fractional_scale_v1 protocol

Giving clients hints about optimal fractional scaling ratios, to be used together with the wp_viewport protocol.

See also:

• https://gitlab.freedesktop.org/wayland/wayland-protocols/-/blob/1.31/staging/fractional-scale/fractional-scale-v1.xml
• !2726
• !2771 (merged)

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Can be tested with:

• weston-simple-egl with https://gitlab.freedesktop.org/wayland/weston/-/merge_requests/1181
• https://gitlab.freedesktop.org/kennylevinsen/fractional-scaling