Parenthesize expressions prior to LibCST parsing (#6742)
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## Summary
This PR adds a utility for transforming expressions via LibCST that
automatically wraps the expression in parentheses, applies a
user-provided transformation, then strips the parentheses from the
generated code. LibCST can't parse arbitrary expression ranges, since
some expressions may require parenthesization in order to be parsed
properly. For example:
```python
option = (
'{name}={value}'
.format(nam=name, value=value)
)
```
In this case, the expression range is:
```python
'{name}={value}'
.format(nam=name, value=value)
```
Which isn't valid on its own. So, instead, we add "fake" parentheses
around the expression.
We were already doing this in a few places, so this is mostly
formalizing and DRYing up that pattern.
Closes https://github.com/astral-sh/ruff/issues/6720.
