Windows: Fix `TooManyParentDirs` handling for paths that shouldn't be cwd-relative

Previously, a relative path like `..` would:
- Attempt to be normalized (i.e. remove . and .. without any path resolution), but would error with TooManyParentDirs
- This would make wToPrefixedFileW run it through `RtlGetFullPathName_U` to do the necessary path resolution, but `RtlGetFullPathName_U` always resolves relative paths relative to the CWD

Instead, when TooManyParentDirs occurs, we now look up the path of the passed in `dir` (if it's non-null) and append the relative path to it before giving it to `RtlGetFullPathName_U`. If `dir` is null, then we just give it RtlGetFullPathName_U directly and let it resolve it relative to the CWD.

Closes #16779

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