docs: Add initial language settings documentation (#6957)

This pull request implements the following documentation changes:

- [x] Copy existing language settings docs from old docs repo
- [x] Add new pages for Zig, Haskell, Gleam, Deno and PureScript
- [x] Add `rust-analyzer` target directory section to Rust language page

Release Notes:

- Added initial language settings documentation
([#4264](https://github.com/zed-industries/zed/issues/4264)).

docs/src/languages/rust.md

@@ -0,0 +1,24 @@
+# Rust
+
+- Tree Sitter: [tree-sitter-rust](https://github.com/tree-sitter/tree-sitter-rust)
+- Language Server: [rust-analyzer](https://github.com/rust-lang/rust-analyzer)
+
+### Target directory
+
+The `rust-analyzer` target directory can be set in `initialization_options`:
+
+```json
+{
+  "lsp": {
+    "rust-analyzer": {
+      "initialization_options": {
+        "rust": {
+          "analyzerTargetDir": true
+        }
+      }
+    }
+  }
+}
+```
+
+A `true` setting will set the target directory to `target/rust-analyzer`. You can set a custom directory with a string like `"target/analyzer"` instead of `true`.