Implement shape folding in the canonicalization pass:

 - Add a few canonicalization patterns to fold memref_cast into
   load/store/dealloc.
 - Canonicalize alloc(constant) into an alloc with a constant shape followed by
   a cast.
 - Add a new PatternRewriter::updatedRootInPlace API to make this more convenient.

SimplifyAllocConst and the testcase is heavily based on Uday's implementation work, just
in a different framework.

PiperOrigin-RevId: 218361237