[flake8-use-pathlib] Add fix safety section to PTH201 (#18837)

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## Summary

<!-- What's the purpose of the change? What does it do, and why? -->

Part of #15584

This adds a `Fix safety` section to [path-constructor-current-directory
(PTH201)](https://docs.astral.sh/ruff/rules/path-constructor-current-directory/#path-constructor-current-directory-pth201)

I could not track down the original PR as this rule is so old it has
gone through several large ruff refactors.
The unsafety is determined here:

d9266284df/crates/ruff_linter/src/rules/flake8_use_pathlib/rules/path_constructor_current_directory.rs (L55-L59)
Unsafe code example:
[playground](https://play.ruff.rs/76da532a-c7ad-4ef9-bba3-4626296e5317)
```py
from pathlib import Path
Path(#
    "."#
)
```

## Test Plan

<!-- How was it tested? -->

N/A, no tests/functionality affected

crates/ruff_linter/src/rules/flake8_use_pathlib/rules/path_constructor_current_directory.rs

@@ -33,6 +33,10 @@ use crate::{AlwaysFixableViolation, Applicability, Edit, Fix};
 /// _ = Path()
 /// ```
 ///
+/// ## Fix safety
+/// This fix is marked unsafe if there are comments inside the parentheses, as applying
+/// the fix will delete them.
+///
 /// ## References
 /// - [Python documentation: `Path`](https://docs.python.org/3/library/pathlib.html#pathlib.Path)
 #[derive(ViolationMetadata)]