Indent guides can be configured per language, meaning that in a multi
buffer we can get excerpts where indent guides should be
disabled/enabled/styled differently than other excerpts.

Imagine the following scenario, i have indent guides disabled in my
settings, but want to enable them for JS and Python. I also want to use
a different line width for python files. Something like this is now
supported:

<img width="445" alt="image"
src="https://github.com/zed-industries/zed/assets/53836821/0c91411c-145c-4210-a883-4c469d5cb828">

And the relevant settings for the example above:
```json
"indent_guides": {
  "enabled": false
},
"languages": {
  "JavaScript": {
    "indent_guides": {
      "enabled": true
    }
  },
  "Python": {
    "indent_guides": {
      "enabled": true,
      "line_width": 5
    }
  }
}
```



Release Notes:

- Respect language specific settings when showing indent guides in a
multibuffer
- Fixes an issue where indent guide specific settings were not
recognized when specified in local settings