## Summary
This PR adds a new precedence level for the comprehension element. This fixes
the generator to not add parentheses around the comprehension element every
time.
The new precedence level is `COMPREHENSION_ELEMENT` and it should occur after
the `NAMED_EXPR` precedence level because named expressions are always parenthesized.
This matches the behavior of Python `ast.unparse` and tested with the
following snippet:
```python
import ast
code = ""
ast.unparse(ast.parse(code))
```
## Test Plan
Add a bunch of test cases for all the valid nodes at that position.
fixes: #5777
