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

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

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:

## 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`.