feat(path): fnamemodify(':h') preserves logical root #40447

Problem:
On Windows, `fnamemodify('//foo/C$', ':h')` incorrectly removes `C$`
as a regular file name and returns `//foo`. However, this is a valid
UNC path, `foo` is a server name and `C$` is a share name.
The correct result should be `//foo/C$`.

Solution:
Extend `os_fileinfo2` and `FileInfo` with `prefix_off`, `rest_off` to
identify path types and logical root boundaries. ':h' can use this info
to prevent traversing past the logical root.

Examples:
  /foo               => /
  //foo              => // (POSIX)
  //foo/bar          => //foo (POSIX)
  //server/share/foo => //server/share/ (Windows)
  C:/foo             => C:/
  //?/C:/foo         => //?/C:/

Co-authored-by: Barrett Ruth <br@barrettruth.com>

0 files changed, 0 insertions, 0 deletions