[mlir][test] Shard the Test Dialect (NFC)

This PR uses the new op sharding mechanism in tablegen to shard the test
dialect's op definitions. This breaks the definition of ops into
multiple source files, speeding up compile time of the test dialect
dramatically. This improves developer cycle times when iterating on the
test dialect.

stack-info: PR: https://github.com/llvm/llvm-project/pull/89628, branch: users/Mogball/stack/1