Address open PR #7404 review feedback:
- Rename CheckInvariants.h/.cpp to InvariantRunner.h/.cpp; the old name
read as invariants for the Checks (ttCHECK*) feature.
- Remove the InvariantCheck interface and Transactor::InvariantCheckAdapter
wrapper. The free checkInvariants runner now takes an optional
Transactor& directly and calls visitInvariantEntry/finalizeInvariants on
it, since the adapter only existed to bridge to a single concrete type.