This PR updates the indicator for changes within a fold to use the
correct color from the theme:

<img width="380" alt="Screenshot 2024-01-08 at 12 52 56 PM"
src="https://github.com/zed-industries/zed/assets/1486634/b8bf6bf3-6acc-43a4-8c4b-a02c975c7f02">

Release Notes:

- Updated the color of the indicator for a fold containing modified
lines.

This PR updates the styling of the tree branches in the current call
section of the collab panel:

- Fixed the gap between the notes and chat items.
- We now overdraw the tree branch on the notes item so it fills the gap.
- The tree branch lines are now thinner.

<img width="231" alt="Screenshot 2024-01-08 at 12 35 35 PM"
src="https://github.com/zed-industries/zed/assets/1486634/844c9e18-c2de-4163-9384-41d1577e23a0">

Note: I think the signature for `render_tree_branch` could use some
improvement. I don't like having the multiple `bool` parameters, but any
change I could think of was going to be a bit more invasive than I
wanted to take on in this PR.

Release Notes:

- Improved the style of the tree branches in current call details in the
collab panel.

Commenting this one out temporarily to not break CI for folks while I
look into it.
Release Notes:

- N/A

Fixes some issues with the Checking icon I added last week.

- Use default text color for "Checking..." text and icon
- Always show text and icon while checks are running

I think we should probably remove the `✅` while checks are running as it
incorrectly indicates nothing is wrong when we don't yet know that – but
that is a larger change so I'll keep this fix contained.

Release Notes:

- Fixes "Checking" diagnostics icon only showing until the first
diagnostics item is found.

This PR tweaks the message role indicator in the assistant panel.

Previously we added a negative margin in #3925 to align the indicator
with the text, but the result of this was the left side of the button
getting clipped on hover.

To remedy this, we now use the filled button style so that the
background always shows and maintains the visual alignment.

### Before

<img width="451" alt="Screenshot 2024-01-08 at 10 50 21 AM"
src="https://github.com/zed-industries/zed/assets/1486634/dd3ae3dc-13c5-4d81-abd7-8023aca496c8">

### After

<img width="401" alt="Screenshot 2024-01-08 at 10 54 42 AM"
src="https://github.com/zed-industries/zed/assets/1486634/c089a879-1c88-4d94-9532-4e9433a35828">

We could also do what we did in Zed1, where the hover style doesn't have
any padding and is flush with the left side of the text, but I don't
think this looks as polished.

The "Assistant" role now also uses a separate color from "System".

Release Notes:

- Updated the style of the message role indicator in the assistant
panel.

This fixes the left side of the button getting clipped on hover.

Release notes
- Fixed double clicking on pane drag handle not resetting pane's split
size.
- Fixed pane group sizes not being serialized.

At present 3 tests still fail; 2 are related to keymap issues that (I
believe) @maxbrunsfeld is working on. The other one
(`test_open_paths_action`) I'll look into. edit: done
This PR also fixes workspace unregistration, as we've put the code to do
that behind `debug_assert`
(https://github.com/zed-industries/zed/pull/3907/files#diff-041673bbd1947a35d45945636c0055429dfc8b5985faf93f8a8a960c9ad31e28L649).
Release Notes:
- N/A

This commit mostly fixes invalid URLs in docstrings. It also
encapsulates crates we reexport (serde stuff + linkme) into a public
module named "private" in order to reduce the API surfaced through docs.
Moreover, I fixed up a bunch of crates that were pulling serde_json in
through gpui explicitly instead of using Cargo manifest.

Release Notes:
- N/A

Deals with https://github.com/zed-industries/community/issues/1856

Release Notes:

- Fixed terminal tab tooltip being truncated

Deals with https://github.com/zed-industries/community/issues/1317
Deals with https://github.com/zed-industries/community/issues/486

Reworks pane drag and drop code to support 
* dropping external files into main pane (supports splits same as tabs
and project entries drop) — this will open the file dropped
* dropping external files, tabs and project entries drop into the
terminal — this will add file abs path into the terminal

Release Notes:

- Added a way to drag and drop external files into Zed main & terminal
panes; support tabs and project entries drop into terminal pane

# TODO

- [x] Fix busted tests
- [x] Check all events from actions on welcome screen
    - [x] change theme
    - [x] change keymap
    - [x] install cli
    - [x] enable vim
    - [x] send metric data
    - [x] send diagnostics
    - [x] close welcome screen
- [X] Check all settings events
    - [x] record theme change (in main and in selector)
    - [x] record base keymap change (in main and in selector)
    - [x] record metric data value
    - [x] record diagnostics value
- [X] Triple check that telemetry settings still block events from being
sent, since we updated how we check for settings changes
- [X] Remove immediate flush mode and allow the flush method to be
called publicly
- [x] Remove references to clickhouse in the code (should be generic at
the client level)

Release Notes:

- N/A

The client sends events to our end point, and the endpoint is what determines what analytics database is used to store the data. The client should be generic and not mention the name of the service being proxied to through our server.

Allow flush method to be called publicly. This is a better, simpler solution, that allows for better control over flushing.

I essentially went through the publicly exported items and marked these
that are e.g. leaky reexports as pub(crate). I expect that'd be done on
Tuesday anyways.

Release Notes:
- N/A

Deals with https://github.com/zed-industries/community/issues/2367

Release Notes:

- Fixed file finder crashing on certain paths with multi-codepoint
characters
([#2367](https://github.com/zed-industries/community/issues/2367))

Release Notes:

- Fixed a bug that was causing Zed to use a lot of energy when moving
the mouse.

Release Notes:

- N/A

Release Notes:

- Fixed base keymap selector keyboard shortcuts

![CleanShot 2024-01-05 at 17 30
11@2x](https://github.com/zed-industries/zed/assets/1789/b70226d0-bc07-4ce3-b45d-c25aace998c2)

Release Notes:

- Fixed the alignment of the assistant headers and text
- Increased the left padding on the assistant.

Since the message headers are buttons, we need to shift them relatively to
compensate for the fact that the background is only visible when hovered.
I'm ok with the background not being aligned so long as the unhovered text is.

Release Notes:

- Restored collab button tooltips, made screenshare item background of
editor background's color