Improve process to pass box shadow color.

[Shinyzenith]

The fact that box_shadow color a float * instead of just a float [4] is problematic.
Wrapping that in FFI is clunky because essentially in zig I need to wrap it as: *f32[4] which might as well just be f32[4].
Not to mention other languages where that kind of pointer arithmetic is usually not suggested. Eg: Python

Why can't we approach it as just float [4]?

[ErikReider]

We could use the wlr_render_color struct instead :)

[ErikReider]

Lol, apparently I fixed this back in January xD