editor: Current line highlight options (#11710)

None:

<img width="717" alt="none"
src="https://github.com/zed-industries/zed/assets/2101250/b2a741db-c64a-4275-a612-5a0d15c9cab7">

Gutter:

<img width="715" alt="gutter"
src="https://github.com/zed-industries/zed/assets/2101250/f7a68a6e-6eba-41b4-9042-5a5fe2ee21a4">

Line:

<img width="717" alt="line"
src="https://github.com/zed-industries/zed/assets/2101250/117f5b00-abd7-425b-8047-1a6fab8293a7">

All:

<img width="715" alt="all"
src="https://github.com/zed-industries/zed/assets/2101250/ebccc0da-0fa0-44e5-903c-cc49d975db76">

This PR adds the `current_line_highlight` setting that defines how to
highlight the current line in the editor:

- `none`: Don't highlight the current line.
- `gutter`: Highlight the gutter area only.
- `line`: Highlight the editor area only.
- `all` (default): Highlight the whole line.

The options have been borrowed from VSCode.

Fixes #5222
Part of #4382

Release Notes:

- Added the `current_line_highlight` setting that defines how to
highlight the current line in the editor (#5222).

docs/src/configuring-zed.md

@@ -186,6 +186,38 @@ left and right padding of the central pane from the workspace when the centered
 
 List of `string` values
 
+## Current Line Highlight
+
+- Description: How to highlight the current line in the editor.
+- Setting: `current_line_highlight`
+- Default: `all`
+
+**Options**
+
+1. Don't highlight the current line:
+
+```json
+"current_line_highlight": "none"
+```
+
+2. Highlight the gutter area.
+
+```json
+"current_line_highlight": "gutter"
+```
+
+3. Highlight the editor area.
+
+```json
+"current_line_highlight": "line"
+```
+
+4. Highlight the full line.
+
+```json
+"current_line_highlight": "all"
+```
+
 ## Cursor Blink
 
 - Description: Whether or not the cursor blinks.