I went to add in `zprofile` to the bash language config to get syntax
highlighting for it. After adding it in, Zed was still not highlighting
the file. I checked and saw that we are using `Path::extension()` in
`language_for_file()`, which [returns `None` when a file's name begins
with a
`.`](https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.extension),
such as in the case of `.zprofile`. This PR adds a custom method, with
some tests, that just tries to grab the last component in the file name
if `Path::extension` returns `None`. Not sure if `ext` is the best name,
but I can't use `extension`.

Maybe this method should be called `extension_or_hidden_file_name()`?

Release Notes:

- Fixed a bug where language detection would fail for files starting
with `.` in their names.
- Added syntax highlighting for `.zprofile` files