…ke 2)

## Filtered recursive walk

Expanding a recursive `**` segment entails walking the entire directory
tree, and so any subsequent pattern segments (except special segments) can
be evaluated by filtering the expanded paths through a regex. For example,
`glob.glob("foo/**/*.py", recursive=True)` recursively walks `foo/` with
`os.scandir()`, and then filters paths through a regex based on "`**/*.py`,
with no further filesystem access needed.

This fixes an issue where `glob()` could return duplicate results.

## Tracking path existence

We store a flag alongside each path indicating whether the path is
guaranteed to exist. As we process the pattern:

- Certain special pattern segments (`""`, `"."` and `".."`) leave the flag
  unchanged
- Literal pattern segments (e.g. `foo/bar`) set the flag to false
- Wildcard pattern segments (e.g. `*/*.py`) set the flag to true (because
  children are found via `os.scandir()`)
- Recursive pattern segments (e.g. `**`) leave the flag unchanged for the
  root path, and set it to true for descendants discovered via
  `os.scandir()`.

If the flag is false at the end, we call `lstat()` on each path to filter
out missing paths.

## Minor speed-ups

- Exclude paths that don't match a non-terminal non-recursive wildcard
  pattern _prior_ to calling `is_dir()`.
- Use a stack rather than recursion to implement recursive wildcards.
  - This fixes a recursion error when globbing deep trees.
- Pre-compile regular expressions and pre-join literal pattern segments.
- Convert to/from `bytes` (a minor use-case) in `iglob()` rather than
  supporting `bytes` throughout. This particularly simplifies the code
  needed to handle relative bytes paths with `dir_fd`.
- Avoid calling `os.path.join()`; instead we keep paths in a normalized
  form and append trailing slashes when needed.
- Avoid calling `os.path.normcase()`; instead we use case-insensitive regex
  matching.

## Implementation notes

Much of this functionality is already present in pathlib's implementation
of globbing. The specific additions we make are:

1. Support for `dir_fd`
2. Support for `include_hidden`
3. Support for generating paths relative to `root_dir`

This unifies the implementations of globbing in the `glob` and `pathlib`
modules.

Co-authored-by: Pieter Eendebak <pieter.eendebak@gmail.com>
Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>