Now that we have both AnimationPlayer and Animation in use we need to clarify
which object we are referring to. This patch renames a number of member and
local variables to better reflect whether they point to an AnimationPlayer or an
Animation.
This patch is mostly renaming only with one exception. Since we are touching
a number of local variables used in loops (for looping over the array of
animation players) we take the opportunity to replace a number of instances of
uint32_t with size_t since that is the preferred type for array indices now.