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/SUMMARY.md

@@ -24,12 +24,42 @@
 
 # Language Support
 
+- [Astro](./languages/astro.md)
+- [C](./languages/c.md)
+- [C++](./languages/cpp.md)
+- [C#](./languages/csharp.md)
+- [Clojure](./languages/clojure.md)
+- [CSS](./languages/css.md)
+- [Deno](./languages/deno.md)
 - [Elixir](./languages/elixir.md)
+- [Elm](./languages/elm.md)
+- [Erlang](./languages/erlang.md)
+- [Gleam](./languages/gleam.md)
 - [Go](./languages/go.md)
+- [Haskell](./languages/haskell.md)
+- [HTML](./languages/html.md)
 - [JavaScript](./languages/javascript.md)
+- [JSON](./languages/json.md)
+- [Lua](./languages/lua.md)
+- [Markdown](./languages/markdown.md)
+- [OCaml](./languages/ocaml.md)
+- [PHP](./languages/php.md)
+- [Prisma](./languages/prisma.md)
+- [Proto](./languages/proto.md)
+- [PureScript](./languages/purescript.md)
 - [Python](./languages/python.md)
+- [Racket](./languages/racket.md)
 - [Ruby](./languages/ruby.md)
 - [Rust](./languages/rust.md)
+- [Scheme](./languages/scheme.md)
+- [Svelte](./languages/svelte.md)
+- [Terraform](./languages/terraform.md)
+- [TOML](./languages/toml.md)
+- [TypeScript](./languages/typescript.md)
+- [Uiua](./languages/uiua.md)
+- [Vue](./languages/vue.md)
+- [YAML](./languages/yaml.md)
+- [Zig](./languages/zig.md)
 
 # Developing Zed