Improve extension API documentation (#10210)

This PR adds more documentation for various constructs in the
`zed_extension_api` crate.

`wit_bindgen` is able to generate doc comments on the Rust constructs
using the the doc comments in the WIT files, so we're able to leverage
that for the majority of the constructs that we expose.

Release Notes:

- N/A

crates/extension_api/src/extension_api.rs

@@ -1,3 +1,5 @@
+//! The Zed Rust Extension API allows you write extensions for [Zed](https://zed.dev/) in Rust.
+
 use core::fmt;
 
 use wit::*;
@@ -8,10 +10,10 @@ use wit::*;
 // that we may want to shadow to provide a cleaner Rust API.
 pub use wit::{
     current_platform, download_file, latest_github_release, make_file_executable, node_binary_path,
-    npm_install_package, npm_package_installed_version, npm_package_latest_version,
-    zed::extension::lsp, Architecture, CodeLabel, CodeLabelSpan, CodeLabelSpanLiteral, Command,
-    DownloadedFileType, EnvVars, GithubRelease, GithubReleaseAsset, GithubReleaseOptions,
-    LanguageServerInstallationStatus, Os, Range, Worktree,
+    npm_install_package, npm_package_installed_version, npm_package_latest_version, Architecture,
+    CodeLabel, CodeLabelSpan, CodeLabelSpanLiteral, Command, DownloadedFileType, EnvVars,
+    GithubRelease, GithubReleaseAsset, GithubReleaseOptions, LanguageServerInstallationStatus, Os,
+    Range, Worktree,
 };
 
 // Undocumented WIT re-exports.
@@ -21,6 +23,14 @@ pub use wit::{
 #[doc(hidden)]
 pub use wit::Guest;
 
+/// Constructs for interacting with language servers over the
+/// Language Server Protocol (LSP).
+pub mod lsp {
+    pub use crate::wit::zed::extension::lsp::{
+        Completion, CompletionKind, InsertTextFormat, Symbol, SymbolKind,
+    };
+}
+
 /// A result returned from a Zed extension.
 pub type Result<T, E = String> = core::result::Result<T, E>;
 
@@ -75,6 +85,9 @@ pub trait Extension: Send + Sync {
     }
 }
 
+/// Registers the provided type as a Zed extension.
+///
+/// The type must implement the [`Extension`] trait.
 #[macro_export]
 macro_rules! register_extension {
     ($extension_type:ty) => {
@@ -165,6 +178,7 @@ impl wit::Guest for Component {
     }
 }
 
+/// The ID of a language server.
 #[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Clone)]
 pub struct LanguageServerId(String);