PR #121478 added options for blurred shadows and text outline for text strips.
However since text strips produce an image that is size of the "whole screen",
applying large blurs or wide outline on that is quite costly.
Make both blur and outline calculations only be performed on the text bounds
(offset and expanded as needed to take into account blur/outline width).
On Windows/VS2022/Ryzen5950X machine, with 4K VSE resolution, and text strip
that takes about 900x400 pixels on screen, applying blur 0.4 and outline 0.25,
time to render the text strip goes from 470ms down to 35ms.
Pull Request: https://projects.blender.org/blender/blender/pulls/121644
a17ce1a1b4