Add clip-shadow-above configuration and wintype option

[tryone144]

Added the new shadow-crop-window configuration option and crop-shadow wintype option. These allow the user to select windows to crop from the shadow region of other windows, i.e. don't paint shadows on top of them.

This should provide a more useful and user friendly alternative to the deprecated shadow-exclude-reg option.
See #494 and #582 (comment).

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The name of this new option is up for debate. My rationale behind not calling it shadow-exclude-window was to avoid confusion with the similarly named shadow-exclude option that disables the shadow that a window casts. In contrast, the new option prevents shadows from being cast onto the target window.
I am not a native speaker, so if crop does not intuitively convey they right meaning, clip might work as well (or trim, truncate, …).

EDIT: Renamed the options to clip-shadow-above.

[codecov]

Codecov Report

Merging #656 (4b5cc05) into next (98fe899) will decrease coverage by 0.10%.
The diff coverage is 58.06%.

@@            Coverage Diff             @@
##             next     #656      +/-   ##
==========================================
- Coverage   39.33%   39.23%   -0.11%     
==========================================
  Files          46       46              
  Lines        9581     9612      +31     
==========================================
+ Hits         3769     3771       +2     
- Misses       5812     5841      +29     

Impacted Files	Coverage Δ
src/config.h	23.52% <ø> (ø)
src/options.c	21.34% <0.00%> (-0.19%)	⬇️
src/render.c	4.09% <0.00%> (-0.05%)	⬇️
src/win.h	78.12% <ø> (ø)
src/backend/backend.c	63.35% <71.42%> (+0.36%)	⬆️
src/config.c	42.74% <100.00%> (+0.70%)	⬆️
src/config_libconfig.c	58.47% <100.00%> (+0.49%)	⬆️
src/picom.c	67.80% <100.00%> (-0.58%)	⬇️
src/win.c	68.13% <100.00%> (-0.73%)	⬇️
... and 1 more

[yshui]

Thanks for implementing this!

As for the name, I am not sure either. I am thinking about something like above-shadow, meaning the window will be above shadows, what do you think? Otherwise I think clip-shadow is probably better.

[tryone144]

After giving this some more thought, I think clip-shadow-above for the rules and wintype option might be a more descriptive name. Would you be fine with this?
I am not too keen on implying the window is actually above the shadow, as it technically isn't which becomes obvious for transparent windows.

Apart from the name change, I am probably going to rebase this on top of the changes in #657.

[yshui]

@tryone144 Yeah, that sounds good 👍

[tryone144]

Renamed to clip-shadow-above and rebased.
Merging this should provide a solution to #494 and (possibly) #4.

[yshui]

Thank you!

[joaopauloalbq]

Any possibility to clip shadow above shadow and thus avoid overlapping shadows?