Add a function to determine whether an op is inside a StableHLO op with `Region`.
Add a function to determine whether an op is inside a StableHLO op with `Region`.

This will be used for filtering target lift patterns in `TableGen` file.

Additionally, this CL does the following:
* Use the `Operation*` than reference-by-value for consistency with MLIR norm.
* Adds additional tests for `IsStablehlOp`.
