Extension refactor (#20305)

This contains the main changes to the extensions crate from #20049. The
primary goal here is removing dependencies that we can't include on the
remote.


Release Notes:

- N/A

---------

Co-authored-by: Mikayla <mikayla@zed.dev>
Co-authored-by: Marshall Bowers <elliott.codes@gmail.com>
Co-authored-by: Marshall <marshall@zed.dev>

crates/indexed_docs/Cargo.toml

@@ -30,6 +30,7 @@ paths.workspace = true
 serde.workspace = true
 strum.workspace = true
 util.workspace = true
+extension_host.workspace = true
 
 [dev-dependencies]
 indoc.workspace = true

crates/indexed_docs/src/providers/rustdoc.rs

@@ -2,6 +2,7 @@ mod item;
 mod to_markdown;
 
 use cargo_metadata::MetadataCommand;
+use extension_host::DocsDatabase;
 use futures::future::BoxFuture;
 pub use item::*;
 use parking_lot::RwLock;
@@ -208,7 +209,7 @@ impl IndexedDocsProvider for DocsDotRsProvider {
 
 async fn index_rustdoc(
     package: PackageName,
-    database: Arc<IndexedDocsDatabase>,
+    database: Arc<dyn DocsDatabase>,
     fetch_page: impl Fn(&PackageName, Option<&RustdocItem>) -> BoxFuture<'static, Result<Option<String>>>
         + Send
         + Sync,

crates/indexed_docs/src/store.rs

@@ -324,8 +324,10 @@ impl IndexedDocsDatabase {
             Ok(any)
         })
     }
+}
 
-    pub fn insert(&self, key: String, docs: String) -> Task<Result<()>> {
+impl extension_host::DocsDatabase for IndexedDocsDatabase {
+    fn insert(&self, key: String, docs: String) -> Task<Result<()>> {
         let env = self.env.clone();
         let entries = self.entries;