Include soft keywords for `is_keyword` check (#11445)
## Summary
This PR updates the `TokenKind::is_keyword` check to include soft
keywords. To account for this change, it adds a new
`is_non_soft_keyword` method.
The usage in logical line rules were updated to use the
`is_non_soft_keyword` method but it'll be updated to use `is_keyword` in
a follow-up PR (#11446).
While, the parser usages were kept as is. And because of that, the
snapshots for two test cases were updated in a better direction.
## Test Plan
`cargo insta test`
