gbm-kms: Make cursor transitions across outputs smoother

[ehopperdietzel]

Keep hardware cursor planes visible on all outputs intersected by the cursor geometry instead of only its position.

Issue: #3449

[RAOF]

Oh, yeah. This seems like a good idea.

This change introduces a test failure in MesaCursorTest.move_to_moves_cursor_to_right_output (presumably because the behaviour is now that the cursor is on both outputs, because it spans both outputs). Would you like to fix that up so I can approve this?

[ehopperdietzel]

Sure, no problem

[ehopperdietzel]

presumably because the behaviour is now that the cursor is on both outputs, because it spans both outputs

Exactly, the test outputs are too small hahaha, but now it should be fixed.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.23%. Comparing base (0980da3) to head (ddb613c).
Report is 407 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3451      +/-   ##
==========================================
- Coverage   77.24%   77.23%   -0.01%     
==========================================
  Files        1071     1071              
  Lines       68467    68468       +1     
==========================================
- Hits        52886    52884       -2     
- Misses      15581    15584       +3     

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[AlanGriffiths]

Works for me