Lanai - MTLClip.beginShapeClip method uses a larger temporary buffer than needed

This method allocates and uses a temporary buffer of size (width * height * 4) - whereas the stencil buffer is of type MTLPixelFormatR8Uint - indicating it is a byte buffer.
It is like we are allocating the temporary buffer which is 4 times larger and filling it with 0's - but using only 1/4th of it to copy.