Inline git blame (#10398)

This adds so-called "inline git blame" to the editor that, when turned
on, shows `git blame` information about the current line inline:


![screenshot-2024-04-15-11 29
35@2x](https://github.com/zed-industries/zed/assets/1185253/21cef7be-3283-4556-a9f0-cc349c4e1d75)


When the inline information is hovered, a new tooltip appears that
contains more information on the current commit:


![screenshot-2024-04-15-11 28
24@2x](https://github.com/zed-industries/zed/assets/1185253/ee128460-f6a2-48c2-a70d-e03ff90a737f)

The commit message in this tooltip is rendered as Markdown, is
scrollable and clickable.

The tooltip is now also the tooltip used in the gutter:

![screenshot-2024-04-15-11 28
51@2x](https://github.com/zed-industries/zed/assets/1185253/42be3d63-91d0-4936-8183-570e024beabe)


## Settings

1. The inline git blame information can be turned on and off via
settings:
```json
{
  "git": {
    "inline_blame": {
      "enabled": true
    }
  }
}
```
2. Optionally, a delay can be configured. When a delay is set, the
inline blame information will only show up `x milliseconds` after a
cursor movement:
```json
{
  "git": {
    "inline_blame": {
      "enabled": true,
      "delay_ms": 600
    }
  }
}
```
3. It can also be turned on/off for the current buffer with `editor:
toggle git blame inline`.

## To be done in follow-up PRs

- [ ] Add link to pull request in tooltip
- [ ] Add avatars of users if possible

## Release notes

Release Notes:

- Added inline `git blame` information the editor. It can be turned on
in the settings with `{"git": { "inline_blame": "on" } }` for every
buffer or, temporarily for the current buffer, with `editor: toggle git
blame inline`.

assets/settings/default.json

@@ -390,7 +390,15 @@
     //      "git_gutter": "tracked_files"
     // 2. Hide the gutter
     //      "git_gutter": "hide"
-    "git_gutter": "tracked_files"
+    "git_gutter": "tracked_files",
+    // Control whether the git blame information is shown inline,
+    // in the currently focused line.
+    "inline_blame": {
+      "enabled": false
+      // Sets a delay after which the inline blame information is shown.
+      // Delay is restarted with every cursor movement.
+      // "delay_ms": 600
+    }
   },
   "copilot": {
     // The set of glob patterns for which copilot should be disabled