wayland-server: alive check for Weak

[cmeissl]

In smithay we quite extensively use Weak as the key for caching some other resource. Cleaning up these resources
often requires checking if the key is still alive. Without an explicit function to check Weak for alive we have to resort to Weak::upgrade().is_ok(). An explicit function can save us from actually upgrading the resource itself, saving us quite some cpu time.

[codecov]

Codecov Report

Attention: Patch coverage is 44.44444% with 5 lines in your changes are missing coverage. Please review.

Project coverage is 75.92%. Comparing base (1f6f4f5) to head (831899a).
Report is 1 commits behind head on master.

❗ Current head 831899a differs from pull request most recent head 85f69b8. Consider uploading reports for the commit 85f69b8 to get more accurate results

Files	Patch %	Lines
wayland-server/src/lib.rs	0.00%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #720      +/-   ##
==========================================
+ Coverage   73.11%   75.92%   +2.81%     
==========================================
  Files          45       45              
  Lines        8183     8192       +9     
==========================================
+ Hits         5983     6220     +237     
+ Misses       2200     1972     -228     

Flag	Coverage Δ
main	58.90% <44.44%> (-0.02%)	⬇️
test--	81.00% <44.44%> (?)
test--server_system	64.64% <44.44%> (?)
test-client_system-	72.15% <44.44%> (?)
test-client_system-server_system	54.97% <44.44%> (-0.02%)	⬇️

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[elinorbgr]

Could you split out the rustfmt changes into another PR? Looks like the check-minimal CI is unhappy about something so I'd prefer we split this to figure out what's going on.

Other than that, LGTM 👍

[ids1024]

#722 should fix the CI failure if this is rebased.

[cmeissl]

sorry for late reply, ran out of time trying to fix the CI build. dropped the commit with the attempt to fix the CI as it is already fixed in master, thx :)