[fx] make sure args/kwargs are immutable (#46121)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/46121
Otherwise, mutating them would make the uses/users lists inaccurate.
You can still mutate the node by assigning a new value to .args or .kwargs
Test Plan: Imported from OSS
Reviewed By: jamesr66a
Differential Revision: D24232288
Pulled By: zdevito
fbshipit-source-id: c95b1a73ae55ad9bdb922ca960c8f744ff732100
