Avoid some `std::string` construction in `ClassTable`.

Do not construct a `std::string` when compaing most class
descriptors for `Class` objects. We still construct it for
the edge case when comparing a proxy class and non-proxy
class descriptors which should really yield false, except
that ART does not propely enforce the namespace separation.

Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Bug: 338123769
Change-Id: I001abf9dd6648621e86f43a8234d2c0c1d02471c
3 files changed