Move fuser to test_jit_fuser (#18590)
Summary:
Start of breaking up test_jit.py
New files will have the format test_jit_* so they are easily grepable but remain in the same directory so we don't have to go through multiple sources for imports.
I am adding a test that's expected to fail to be sure it's running.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/18590
Reviewed By: wanchaol
Differential Revision: D14677094
Pulled By: eellison
fbshipit-source-id: 9782c6aa9525bb6f332fc75cfff004c83a417522
