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/zig.md

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