add itt unit test and docstrings (#84848)
Add unit tests and docstrings corresponding to PR https://github.com/pytorch/pytorch/pull/63289
UT:
1. `test_profiler_emit_itt` in `test/test_autograd.py`. This test is merely intended to catch if emit_itt breaks on construction.
2. Test `torch.profiler.itt` functions in `test/test_itt.py`
3. Only testing that emit_itt runs when `record_shapes` option is enabled in `test/test_profiler.py`.
Docstring:
1. add ITT related info into `docs/source/bottleneck.rst`
4. add `torch.profiler.itt` functions to `docs/source/profiler.rst`
5. add docstring to `torch.profiler.itt` functions in `torch/profiler/itt.py`
Pull Request resolved: https://github.com/pytorch/pytorch/pull/84848
Approved by: https://github.com/malfet
