[MLIR] Rename MemRefBoundCheck.cpp -> TestMemRefBoundCheck.cpp

Summary:

This makes it consistent with other test passes.

Reviewers: rriddle

Reviewed By: rriddle

Subscribers: merge_guards_bot, mgorny, mehdi_amini, jpienaar, burmako, shauheen, antiagainst, nicolasvasilache, arpith-jacob, mgester, lucyrfox, aartbik, liufengdb, Joonsoo, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D74068