gpu::LaunchOp: canonicalize away constant kernel arguments

The GPU Launch operation may take constants as arguments, in particular
affine-to-GPU mapping pass automatically forwards potentially constant lower
bounds of loops into the kernel.  Define a canonicalization pattern for
LaunchOp that recreates the constants inside the kernel region instead of
accepting them as kernel arguments.  This is currently restricted to standard
constants but may be extended to other constant operations.

Also fix an off-by-one indexing bug in OperandStorage::eraseOperand.

PiperOrigin-RevId: 256035437