Add a command to expand the context for a multibuffer (#10300)

This PR adds an action to expand the excerpts lines of context in a
multibuffer.

Release Notes:

- Added an `editor::ExpandExcerpts` action (bound to `shift-enter` by
default), which can expand the excerpt the cursor is currently in by 3
lines. You can customize the number of lines by rebinding this action
like so:

```json5
// In your keybindings array...
  {
    "context": "Editor && mode == full",
    "bindings": {
      "shift-enter": ["editor::ExpandExcerpts", { "lines": 5 }],
    }
  }
```

---------

Co-authored-by: Nathan <nathan@zed.dev>
Co-authored-by: Max <max@zed.dev>

script/generate-licenses

@@ -7,10 +7,11 @@ OUTPUT_FILE="${1:-$(pwd)/assets/licenses.md}"
 > $OUTPUT_FILE
 
 echo -e "# ###### THEME LICENSES ######\n" >> $OUTPUT_FILE
-
-echo "Generating theme licenses"
 cat assets/themes/LICENSES >> $OUTPUT_FILE
 
+echo -e "# ###### ICON LICENSES ######\n" >> $OUTPUT_FILE
+cat assets/icons/LICENSES >> $OUTPUT_FILE
+
 echo -e "# ###### CODE LICENSES ######\n" >> $OUTPUT_FILE
 
 [[ "$(cargo about --version)" == "cargo-about 0.6.1" ]] || cargo install cargo-about@0.6.1