bugfix: screenshots now respect the GLConfig and contain a depth + stencil buffer when one is required

[mattkae]

fixes #3438

What's new?

• BasicScreenShooter now respects the GLConfig
• When depth and stencil bits are provided, we create a render buffer for them

I was unable to make separate stencil/depth buffers worked, but it is apparently recommended that they are combined. I don't know if this will have any major issues...

[codecov]

Codecov Report

Attention: Patch coverage is 48.00000% with 13 lines in your changes missing coverage. Please review.

Project coverage is 77.23%. Comparing base (b526b15) to head (b486ad8).
Report is 423 commits behind head on main.

Files with missing lines	Patch %	Lines
...latforms/common/server/cpu_copy_output_surface.cpp	0.00%	10 Missing ⚠️
...latforms/eglstream-kms/server/buffer_allocator.cpp	0.00%	1 Missing ⚠️
src/platforms/gbm-kms/server/buffer_allocator.cpp	0.00%	1 Missing ⚠️
...latforms/renderer-generic-egl/buffer_allocator.cpp	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3444      +/-   ##
==========================================
- Coverage   77.24%   77.23%   -0.01%     
==========================================
  Files        1071     1071              
  Lines       68468    68475       +7     
==========================================
- Hits        52890    52889       -1     
- Misses      15578    15586       +8     

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[AlanGriffiths]

looks sensible, and doesn't break anything I tried