Blender Git Loki

NLA: Action Strip Defaults Sync Length On

See T82309#1055564 {T63675} and their duplicates for how Default-off
can cause confusion.

This is just for convenience since it allows animators to keyframe
outside of the strip's bounds by default. This was likely off by
default before since Syncing Length would undesirably shift the whole
animation after leaving tweak mode (fixed by {D7602}) and the animator
wasn't able to keyframe outside the strip bounds anyways
(fixed by {D7533}). Now it's better if the flag was on by default.
While the animator is still roughly developing their animation NLA-wise
they won't have to worry about strip bound keying failures. When they
are more certain of the strip bounds, they can disable the flag to
prevent affecting the rest of the NLA system.

Reviewed By: sybren

Differential Revision: https://developer.blender.org/D9661