[fir][NFC] Move RewritePatterns.td to CanonicalizationPatterns.td in Dialect

RewritePatterns.td/RewritePatterns.inc is used only by the
FIROps.cpp file. This patch move this file logically in the Dialect
folder together with FIRDialet, FIROps, FIRTypes ...
It also rename it to CanonicalizationPatterns.td.

This patch is part of the upstreaming effort from fir-dev branch.

Reviewed By: schweitz

Differential Revision: https://reviews.llvm.org/D112522