[fx] make sure args/kwargs are immutable (#46325)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/46325
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: D24308672
Pulled By: zdevito
fbshipit-source-id: a5305e1d82668b36e46876c3bc517f6f1d03dd78
