Extract ExtensionIndexedDocsProvider to indexed_docs crate (#20607)

This PR extracts the `ExtensionIndexedDocsProvider` implementation to
the `indexed_docs` crate.

To achieve this, we introduce a new `Extension` trait that provides an
abstracted interface for calling an extension. This trait resides in the
`extension` crate, which has minimal dependencies and can be depended on
by other crates, like `indexed_docs`.

We're then able to implement the `ExtensionIndexedDocsProvider` without
having any knowledge of the Wasm-specific internals of the extension
system.

Release Notes:

- N/A

crates/extension_host/src/extension_host.rs

@@ -9,6 +9,7 @@ use async_tar::Archive;
 use client::{telemetry::Telemetry, Client, ExtensionMetadata, GetExtensionsResponse};
 use collections::{btree_map, BTreeMap, HashSet};
 use extension::extension_builder::{CompileExtensionOptions, ExtensionBuilder};
+use extension::Extension;
 pub use extension::ExtensionManifest;
 use fs::{Fs, RemoveOptions};
 use futures::{
@@ -90,10 +91,6 @@ pub fn is_version_compatible(
     true
 }
 
-pub trait DocsDatabase: Send + Sync + 'static {
-    fn insert(&self, key: String, docs: String) -> Task<Result<()>>;
-}
-
 pub trait ExtensionRegistrationHooks: Send + Sync + 'static {
     fn remove_user_themes(&self, _themes: Vec<SharedString>) {}
 
@@ -149,13 +146,7 @@ pub trait ExtensionRegistrationHooks: Send + Sync + 'static {
     ) {
     }
 
-    fn register_docs_provider(
-        &self,
-        _extension: WasmExtension,
-        _host: Arc<WasmHost>,
-        _provider_id: Arc<str>,
-    ) {
-    }
+    fn register_docs_provider(&self, _extension: Arc<dyn Extension>, _provider_id: Arc<str>) {}
 
     fn register_snippets(&self, _path: &PathBuf, _snippet_contents: &str) -> Result<()> {
         Ok(())
@@ -1238,6 +1229,8 @@ impl ExtensionStore {
                 this.reload_complete_senders.clear();
 
                 for (manifest, wasm_extension) in &wasm_extensions {
+                    let extension = Arc::new(wasm_extension.clone());
+
                     for (language_server_id, language_server_config) in &manifest.language_servers {
                         for language in language_server_config.languages() {
                             this.registration_hooks.register_lsp_adapter(
@@ -1280,11 +1273,8 @@ impl ExtensionStore {
                     }
 
                     for (provider_id, _provider) in &manifest.indexed_docs_providers {
-                        this.registration_hooks.register_docs_provider(
-                            wasm_extension.clone(),
-                            this.wasm_host.clone(),
-                            provider_id.clone(),
-                        );
+                        this.registration_hooks
+                            .register_docs_provider(extension.clone(), provider_id.clone());
                     }
                 }