Fix interpolating to identity bone overrides (#16609)

The previous code immediately dropped identity overrides, even if there still was an interpolation to be done.
Also a little bit of cleanup, and setting an appropriate identity default for the scale property when interpolating.

For modders: As a workaround, you can add a tiny offset so that overrides aren't identity overrides.

games/devtest/mods/testentities/visuals.lua

@@ -95,7 +95,7 @@ core.register_entity("testentities:sam", {
 		self.object:set_bone_override("Head", {
 			scale = {
 				vec = vector.new(s, s, s),
-				absolute = true,
+				absolute = false,
 				interpolation = self._head_anim_duration,
 			},
 		})