[BE] Beef up test_functionalization to test functionalizing multi-par…

…ameter functions (pytorch#89798)

Previously, `assert_functionalization` only took in uni-Tensor-parameter functions. This PR beefs up the check to allow for functions that take multiple parameters.

This PR also changes the test_instance_norm test to check that the multiparam change works.

## Test plan
Locally tested, CI should also pass.
Pull Request resolved: pytorch#89798
Approved by: https://github.com/samdow