distributes test (#1118)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/1118

This stack focuses on moving all bundled program codes under executorch/sdk/bundled_program. Target and discussions can be found in D49605947.

This diff distributes tests under corresponding directory. Instead of putting all tests related to `bundled_program` under `bundled_program/tests`, now we move test for specific code directory under it for better structure.

More specific, we move the `test_serialize` under `bundled_program/serialize/test`.
We also move `common.py` under `bundled_program/util` for better structure.

Reviewed By: tarun292

Differential Revision: D50847436

fbshipit-source-id: b4f8810af74e7e2968fac47e62be95c1a6e42e61