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/zed/src/reliability.rs

@@ -495,10 +495,7 @@ async fn upload_panic(
 ) -> Result<bool> {
     *most_recent_panic = Some((panic.panicked_on, panic.payload.clone()));
 
-    let json_bytes = serde_json::to_vec(&PanicRequest {
-        panic: panic.clone(),
-    })
-    .unwrap();
+    let json_bytes = serde_json::to_vec(&PanicRequest { panic }).unwrap();
 
     let Some(checksum) = client::telemetry::calculate_json_checksum(&json_bytes) else {
         return Ok(false);