The 32_32_32_FLOAT format seems to be vertex-only, so it looks like there
can't be storage elements smaller than a single texel.
So, use a more precise name that can't be confused with "picture element"
(pixel) or "texture element" (texel) that represents a single logical pixel
rather than a storage block of pixels.
Switch between even and odd 16-byte element sequences along X by simply
flipping a bit rather than going to a different resolution-scaled group of
pixels, by increasing the size of the group within the constraints imposed
by tiling.
Use the _xe suffix instead of the xesl_ prefix for quicker visual
recognition of identifiers, also switch to snake_case for consistency.
Also add the f suffix to float32 literals because the Metal Shading
Language is based on C++.
