VSE timeline strips now have rounded corners. Strip corner rounding radius is
4, 6 or 8px depending on strip height (if strip is too narrow to fit
rounding, then rounding is turned off).
This is achieved with a dedicated GPU shader for drawing most of VSE
strip widget, that it could do proper rounded corner masking.
More details and images in the PR.
Pull Request: https://projects.blender.org/blender/blender/pulls/122576
