Refactor ClassLinker::FindPrimitiveClass().

Introduce ClassLinker::LookupPrimitiveClass() that never
throws an exception and use it to clean up callers that
are not supposed to cause thread suspension.

Test: m test-art-host-gtest
Bug: 118909457
Change-Id: Ibfee8b7991c4a0d1fa636c85f14437c9865d1658