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/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;