docs: Update language docs and include links in the sidebar (#13828)

This PR updates the supported language docs and adds them to the sidebar
for better discoverability.

Release Notes:

- N/A

docs/src/languages/php.md

@@ -1,4 +1,3 @@
 # PHP
 
-- Tree Sitter: [tree-sitter-php](https://github.com/tree-sitter/tree-sitter-php)
-- Language Server: [intelephense](https://intelephense.com/)
+PHP support is available through the [PHP extension](https://github.com/zed-industries/zed/tree/main/extensions/php).