[wayland] Implement XdgForeign

[PolyMeilex]

This also includes a SCTK test client, not sure if we want that in the codebase, but I committed it for now, we can just drop the commit as needed.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 8.16327% with 180 lines in your changes are missing coverage. Please review.

Project coverage is 20.46%. Comparing base (b62ced7) to head (b33ba0e).

Files	Patch %	Lines
src/wayland/xdg_foreign/handlers.rs	0.00%	162 Missing ⚠️
src/wayland/xdg_foreign/mod.rs	48.27%	15 Missing ⚠️
anvil/src/state.rs	40.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1342      +/-   ##
==========================================
- Coverage   20.55%   20.46%   -0.10%     
==========================================
  Files         158      160       +2     
  Lines       25868    26064     +196     
==========================================
+ Hits         5317     5333      +16     
- Misses      20551    20731     +180     

Flag	Coverage Δ
wlcs-buffer	17.89% <8.16%> (-0.08%)	⬇️
wlcs-core	17.55% <8.16%> (-0.08%)	⬇️
wlcs-output	7.53% <8.16%> (+<0.01%)	⬆️
wlcs-pointer-input	19.34% <8.16%> (-0.09%)	⬇️

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[Drakulix]

This also includes a SCTK test client, not sure if we want that in the codebase, but I committed it for now, we can just drop the commit as needed.

I don't think it's harmful, but it might make a better example for SCTK?

[Drakulix]

LGTM (waiting for a decision regarding the example before merging)

[PolyMeilex]

Test client dropped, SCTK sounds like a better place, as there it can serve both as an example and a test client at the same time.