RFR: Trim down oop-equals verification

[Roman Kennke]

This:
- Renames VerifyStrictOopOperations to VerifyObjectEquals, this catches
the intent better.
- Removes the overrides for oop == void* because this is a case we are
not actually interested in.
- Fixes a bunch of places to not use unsafe_equals() and instead use the
above oop == void* (most of them are actually reverts to upstream code)

Testing: tier3_gc_shenandoah

Ok?

Roman