[fx] When generating names, avoid shadowing builtins (#43653)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/43653
When nodes are created without an explicit name, a name is generated for
it based on the target. In these cases, we need to avoid shadowing
builtin names. Otherwise, code like:
```
a.foo.bar
```
results in pretty-printed code like:
```
getattr = a.foo
getattr_1 = getattr.bar
```
While this is technically allowed in Python, it's probably a bad idea,
and more importantly is not supported by TorchScript (where `getattr` is
hardcoded).
This PR changes the name generation logic to avoid shadowing all
builtins and langauge keywords. We already do this for PyTorch
built-ins, so just extend that logic. So now the generated code will
look like:
```
getattr_1 = a.foo
getattr_2 = getattr_1.bar
```
Fixes #43522
Test Plan: Imported from OSS
Reviewed By: jamesr66a
Differential Revision: D23357420
Pulled By: suo
fbshipit-source-id: 91e9974adc22987eca6007a2af4fb4fe67f192a8
