Batch renames in LowerTypes (#1718)

* Batch renames in LowerTypes

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@ibm.com>

* Add benchmarking for LowerTypes

Add infrastructure of benchmarking Transforms (in addition to
existing infra for Passes). Also run System.gc between each timed
benchmark to improve stability.

Co-authored-by: Jack Koenig <koenig@sifive.com>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>