Support hit object pooling in ScrollingPlayfield
This was causing multiple issues with masking and sizing and really didn't need to exist in the first place. Also not sure why the pool was nested inside the scroll container, but it isn't any more. Probably for the best.
This reverts commit b4cc39149c117e6a0e95ee917a67cec8ba723d06.
Closes #10898.
Using drawables still, just to get things in place and setup the structure
Clear DrawableHitObject transforms on return to pool