test: Expand test coverage of public APIs for all types in ConstantTypedExpr (facebookincubator#14912)

Summary:
Pull Request resolved: facebookincubator#14912

1. Added tests for hash(), serialize() + create() and toString() APIs
2. Tested for consistency between initializing ConstantTypedExpr using either variant and vector as we support both
3. Covered all scalar and complex types including opaque

Reviewed By: peterenescu

Differential Revision: D82837494

fbshipit-source-id: fc368ec7ad732e1b3a722ed550352393153064d6

Author: kKPulla