Add setting to hide active language button in the status bar (#33977)

Release Notes:

- Added settings status_bar.show_active_language_button to show/hide the
language button in the status bar.

The motivation for this is visual, I have had zero issues with its
functionality.

The language switcher can still be accessed by the command palette,
menu, or a keyboard shortcut.

------

This is my first Zed and first Rust PR, so criticism is very welcome. 

I know there has been discussion around how the status bar settings are
structured and named, and I am happy to change it to whatever is best. I
was also not sure what order to put it in in the settings default.json.
Feedback welcome.

Here is a picture of it in action:


![image](https://github.com/user-attachments/assets/c50131e2-71aa-4fab-8db0-8b2aae586e71)

---------

Co-authored-by: zumbalogy <3770982+zumbalogy@users.noreply.github.com>
Co-authored-by: Kirill Bulatov <kirill@zed.dev>

assets/settings/default.json

@@ -1238,6 +1238,11 @@
     // 2. hour24
     "hour_format": "hour12"
   },
+  // Status bar-related settings.
+  "status_bar": {
+    // Whether to show the active language button in the status bar.
+    "active_language_button": true
+  },
   // Settings specific to the terminal
   "terminal": {
     // What shell to use when opening a terminal. May take 3 values: