Refactor code to centralize the logic too

<img width="1608" alt="SCR-20230806-cyrg"
src="https://github.com/zed-industries/zed/assets/19867440/2491c4bc-5797-4417-9633-08c136b4e8fe">

I noticed we weren't highlghting bash files if the shebang line didn't
exist. After checking, it looks like the `.` were accidentally added to
the `path_suffixes` list. This PR fixes that and adds in support for
`cmd-/` to trigger line comments.

<img width="1608" alt="SCR-20230806-czxh"
src="https://github.com/zed-industries/zed/assets/19867440/37dd0c8e-c4e7-49e2-9997-9dd8145f460e">


Release Notes:

- Fixed a bug where shell files weren't syntax highlighted if a shebang
didn't exist.
- Added support for `cmd-/` to add line comments to shell files.

When doing case conversions, specifically in the case of an empty
selection, in both VS Code and Sublime, the cursor winds up being in a
different place relative to where it started.

In VS Code, the cursor maintains it position in the text, no matter if
the text expands or shrinks


https://github.com/zed-industries/zed/assets/19867440/b24f5d86-c315-4a72-9ed4-3732b490ea9a

In Sublime, I have no idea what is going on:


https://github.com/zed-industries/zed/assets/19867440/05f21303-6e42-47b2-b844-7accd0bf05d7

I thought it would be a better experience if, when doing an empty
selection transformation, we simply expand the selection and park the
cursor at the end of the newly-transformed text.


https://github.com/zed-industries/zed/assets/19867440/833619ef-04e2-47b6-ad4e-e2b43d54fb2b

This feels similar to us expanding the selection when doing line
manipulations:


https://github.com/zed-industries/zed/assets/19867440/c30c5332-787d-4cf0-a9ee-e66c3c159956

Selections are adjusted to match however each word expands and shrinks,
even when there are multiple:


https://github.com/zed-industries/zed/assets/19867440/d7073aac-8a59-4f2c-b0e5-1df37be1694c

Release Notes:

- Improved behavior of empty-selection case transformations by selecting
resulting word.
- Fixed some bugs with overflow

I'm using [convert_case](https://crates.io/crates/convert_case)
underneath the hood, which has over 35 million downloads and feels
solid.

Release Notes:

- Added commands to convert between variable name styles
([#1821](https://github.com/zed-industries/community/issues/1821)).
    - `convert to kebab case`
    - `convert to snake case`
    - `convert to upper camel case`
    - `convert to lower camel case`
    - `convert to title case`

ConvertToTitleCase
ConvertToSnakeCase
ConvertToKebabCase
ConvertToUpperCamelCase
ConvertToLowerCamelCase

Co-authored-by: Mikayla <mikayla@zed.dev>

Release Notes:

- Added `convert to upper case` and `convert to lower case` commands
([#1011](https://github.com/zed-industries/community/issues/1011)).

Co-authored-by: Mikayla <mikayla@zed.dev>

Co-Authored-By: Julia <30666851+ForLoveOfCats@users.noreply.github.com>

Instead of using the same row count as for the breadcrumbs, we double the height so that there's some space for padding.

Co-authored-by: Kyle <kyle@zed.dev>

Co-authored-by: Kyle <kyle@zed.dev>

Co-authored-by: Kyle <kyle@zed.dev>

Co-authored-by: Kyle <kyle@zed.dev>

This reverts commit 13a6b65a35b886b9ac380e56354acb7e562bcfab.

Instead of returning a usize for the window id, I'm instead returning a
`WindowHandle<V: View>` where `V` is the type of the window's root view.
@as-cii helped me with a cool technique using generic associated types
where methods on `WindowHandle` can return either T or Option<T>
depending on the `BorrowWindowContext::Result` associated type.

Some example usage...

```rs
let window = cx.add_window(|cx| MyView::new(cx));
let my_view = window.root(cx); // If cx is TestAppContext, returns MyView. Otherwise returns Option<MyView>, because the window could be closed.
```


This isn't insanely beneficial on its own, but I think it will help
clean up our testing story. I'm planning on making `window` more useful
in tests for laying out elements, etc.

- [x] Rework tests that call `add_window` 😅 to expect only a window in
return.
- [x] Get tests passing
- [x] 🚬  test

Co-authored-by: Mikayla <mikayla@zed.dev>

This PR adds a `PathExt` trait. It pulls in our existing `compact()`
function, as a method, and then adds a method, and testing, for
`icon_suffix()`. A test was added to fix:

- https://github.com/zed-industries/community/issues/1877

Release Notes:

- Fixed a bug where file icons would not be registered for files with
with `.` characters in their name
([#1877](https://github.com/zed-industries/community/issues/1877)).

Co-authored-by: Mikayla <mikayla@zed.dev>

Co-authored-by: Kyle <kyle@zed.dev>

Co-authored-by: Kyle <kyle@zed.dev>
Co-authored-by: Max <max@zed.dev>

Co-authored-by: Kyle <kyle@zed.dev>

Co-authored-by: Kyle <kyle@zed.dev>

Co-authored-by: Piotr <piotr@zed.dev>