Blender Git Loki

Fix T36385: Animated Strip-Time doesnt update

This commit implements proper evaluation + keyframing support for animating influence
and time on NLA Strips (among other properties) by resolving a few long standing issues
which prevented the original design for this from working.

The original design for animating these properties (and/or some of the other settings
on NLA Strips) is that NLA Strips actually have some of their own F-Curves that are
used for animating settings which will affect how they are evaluated. As seen in this
bug report, the alternative of having these animated as part of the stack (which the
strips work above/outside/on-top of) means that glitches can occur.

Although one of the original considerations for why this wasn't implemented earlier
was that introducing keyframes there isn't so clean cut, and causes UI design issues
for how we expose these via the animation editors for editing (NOTE: support for that
is still to come). Another concern is that this sets a precedent for how FModifiers
might get evaluated.