Z-2556

/cc @JosephTLyons 

Release Notes:

- N/A

Co-authored-by: maxbrunsfeld <max@zed.dev>

Co-authored-by: maxbrunsfeld <max@zed.dev>

Z-2556

Extract branch list into a separate vcs_menu crate akin to recent_projects.
Add current bind for a modal branch to branch popover's tooltip.

Z-2555

Updates the assistant with some style quality of life changes.

## Changes

Restyled the conversation list

<img width="646" alt="CleanShot 2023-07-10 at 10 25 23@2x"
src="https://github.com/zed-industries/zed/assets/1714999/5c9a4f94-11c1-4d28-8aac-4d38141829a9">

Updated the assistant header to be a bit more compact, and use a new tab
bar icon style. The existing tab bar icons will be updated in a later
PR.

<img width="646" alt="CleanShot 2023-07-10 at 10 26 30@2x"
src="https://github.com/zed-industries/zed/assets/1714999/3ef9a053-59fa-4d34-9b76-3bb2701acb33">

Updated the remaining token indicator to have 3 steps:
<img width="662" alt="CleanShot 2023-07-10 at 10 29 51@2x"
src="https://github.com/zed-industries/zed/assets/1714999/13d31545-5b00-427c-b7da-b4dfeac037d6">

Updated role labels, added a hover state to make it more clear these are
interactive
<img width="984" alt="CleanShot 2023-07-10 at 10 32 28@2x"
src="https://github.com/zed-industries/zed/assets/1714999/24748495-dde4-4ee9-98f1-6a082f0c1d4d">


Release Notes:

- Improved the UI of some elements in the Assistant panel.

Z-2545

Release Notes:

- N/A

It also focuses the first result (just like a normal enter).

Z-2554

Release Notes:

- N/A

Discord can directly render the Markdown now.

As part of this I added `assert_shared_state()` to the
NeovimBackedTestContext so that it is more like a drop-in replacement
for the VimTestContext.

The remaining part of zed-industries/community#682 is adding bracket
matching to plain text. It looks like the current logic requires there
to be a tree sitter language for the language in order to support
bracket matching. I didn't fix this in this PR because I was unsure
whether to try and work around that, or to try and add a plain text tree
sitter language.

Release Notes:

- vim: support `{` and `}` for paragraph motion
([#470](https://github.com/zed-industries/community/issues/470)).
- vim: fix `%` at the end of the line
([#682](https://github.com/zed-industries/community/issues/682)).

A few small tweaks to fix some of the community issues

Release Notes:

- vim: Fix `escape` in command palette
([#1347](https://github.com/zed-industries/community/issues/1347)).
- vim: Allow `^` as a motion in actions
([#856](https://github.com/zed-industries/community/issues/856)).
- vim: Allow `ctrl-c` to exit visual mode
([#1447](https://github.com/zed-industries/community/issues/1447)).

We've been getting a bunch of panics from duplicate app instances
competing over the local sqlite DB. After chatting with @mikayla-maki we
determined it was probably best to add our own mechanism to prevent
duplicates rather than just relying on the OS. My logic is that we'd
need to build a system like this eventually for Windows/Linux anyway so
it's more appealing than reworking our local DB access to be able to
cooperate with another process while likely isn't something we want to
support anyway.

I attempted to keep this mechanism conservative so in the case of
another program interfering with it we should fail somewhat gracefully
and still continue to launch, albeit without the ability to prevent
another instance from launching.

Fixes
https://linear.app/zed-industries/issue/Z-2435/thread-background-executor-1-panicked-at-could-not-send-write-action

Release Notes:
- Added a mechanism to prevent duplicate Zed instances from launching to
avoid a crash.

Z-2545

Mutex::new() is const-stable as of Rust 1.63.

Release Notes:
- N/A

Fixes
https://linear.app/zed-industries/issue/Z-2552/pressing-two-keystrokes-in-rapid-succession-ignores-the-latter

Previously, we would only track whether the previous key down event was
a key equivalent. However, this could cause issues when pressing certain
keystrokes in rapid succession, e.g.:

- Pressing `shift-right` (to select a character, dispatched as a key
equivalent)
- Pressing a character (with or without `shift` held down, dispatched as
a key down)

This would cause GPUI to ignore the second event because it was preceded
by a key equivalent event. With this commit, we track the last key
equivalent event, and skip the key down event only if it matches the
last key equivalent event.

Release Notes:

- Fixed a bug that could cause certain keystrokes performed in rapid
succession to incorrectly get ignored.

Previously, we would only track whether the previous key down event
was a key equivalent. However, this could cause issues when pressing
certain keystrokes in rapid succession, e.g.:

- Pressing `shift-right` (to select a character)
- Pressing a character (with or without `shift` held down)

This would cause GPUI to ignore the second event because it was
preceded by a key equivalent event. With this commit, we track the
last key equivalent event, and skip the key down event only if it
matches the last key equivalent event.

Inlay hints depend on LSP server settings, but servers do not update the
initialization options and query hints with old settings.

Generally, we cannot know whether a certain option can be changed
without server restart, which the name of the options implies too, so be
on the safe side and restart the server.
Hints will update automatically after the server either sends a /refresh
request or reports its work progress end after startup.

Release Notes:

- Fixed LSP server not restarting after `initialization_options`
settings changes

This PR adds highlighting of search results to the scrollbar.

Release Notes:

- Added highlighting of search results to the scrollbar.

Fixes
https://linear.app/zed-industries/issue/Z-2540/filter-out-non-conversation-files-from-the-assistant-history

Fixes inability to do `alt + left arrow` when an inlay with `Bias::Left`
is right to the left of the caret.

Release Notes:

- N/A

This fixes an issue that was causing `alt-left` to not move the cursor
when it was located right after an inlay hint with a `Left` bias.

Closes https://linear.app/zed-industries/issue/Z-2537/inlay-hint-issues

Language servers such as typescript-language-servers report a single
work event, ending right after server's startup.

Other servers might send more similar event, also during startup. The
rest of the events are diagnostic-related and we filter them out.

React on such events with /refresh-like hint update, that will check
only the visible part of the editor for hints and might be replaced by
other /refresh requests, if needed.

Release Notes:

- N/A