end2end test for bundled program (#395)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/395

Update pybinding functions to support bundled program (bp) APIs with method name. Split the end2end test for bp into a single test file.

The reasonsfor spliting are:
1. Current overall end2end test does not support multiple methods, but we need to test bp on multiple methods.
2. Bp does not need to be tested on several different kinds of program.
3. Decompose the test for core ET and Bp.

Reviewed By: tarun292

Differential Revision: D49336485

fbshipit-source-id: 89aa3281771fcd9d283c288651d06e7582fe29e3