move schema files under bundled_program/schema (#1057)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/1057

Pull Request resolved: https://github.com/pytorch/executorch/pull/436

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

This diff moves all bundled program schemas, both py schema and fbs schema, under bundled_program/schema, and update dependencies.

Reviewed By: tarun292

Differential Revision: D50422560

fbshipit-source-id: 10289634f46c657b0f99647659ff0067e06ea314