UI: Use flat colors for NLA strip drawing

The NLA editor is in need of a design overhaul, hopefully for 3.1 or 3.2.

This should be a project on itself, however, the worst offender currently is the use of
gradients on strips. Something that can be fixed easily.

{F11390293, size=full, loop, autoplay}

A simple replace of `UI_draw_roundbox_shade_x` for `UI_draw_roundbox_4fv` brings strips
in line with how other areas are drawn.

This patch also:
* Remove embossed lines around active action channel.
* Highlight the strip while being moved.

This patch does not include any theme changes. This will be tackled separately.

Reviewed By: HooglyBoogly

Differential Revision: https://developer.blender.org/D12968

1 files changed, 0 insertions, 0 deletions

diff --git a/source/tools b/source/tools
-Subproject 7c5acb95df918503d11cfc43172ce1390101928
+Subproject 2e8c879248822c8e500ed49d79acc605e5aa75b