Auto/Combined renderer PoC

[cmeissl]

This is a hand written renderer combining our GlesRenderer and PixmanRenderer to validate and discuss before starting with work on a proc-macro based approach.

To be used in combination with https://github.com/Smithay/smithay/pull/1666

based on https://github.com/Smithay/smithay/pull/1637

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 74.31193% with 28 lines in your changes missing coverage. Please review.

Project coverage is 19.16%. Comparing base (10d03af) to head (cd9c439). Report is 67 commits behind head on master.

Files with missing lines	Patch %	Lines
src/backend/renderer/damage/mod.rs	90.62%	6 Missing :warning:
src/backend/renderer/element/utils/elements.rs	0.00%	6 Missing :warning:
src/backend/renderer/element/texture.rs	0.00%	5 Missing :warning:
src/backend/renderer/test.rs	61.53%	5 Missing :warning:
src/backend/egl/context.rs	0.00%	3 Missing :warning:
src/backend/renderer/element/memory.rs	0.00%	2 Missing :warning:
src/backend/renderer/mod.rs	0.00%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1668      +/-   ##
==========================================
- Coverage   19.18%   19.16%   -0.03%     
==========================================
  Files         174      174              
  Lines       28693    28744      +51     
==========================================
+ Hits         5505     5508       +3     
- Misses      23188    23236      +48     

Flag	Coverage Δ
wlcs-buffer	16.70% <74.31%> (-0.02%)	:arrow_down:
wlcs-core	16.44% <74.31%> (-0.02%)	:arrow_down:
wlcs-output	6.81% <25.68%> (-0.01%)	:arrow_down:
wlcs-pointer-input	18.14% <74.31%> (-0.03%)	:arrow_down:

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