debugger beta: Fix dap_schema for DAP extensions (#31173)

We now actually call dap_schema provided by extensions instead of
defaulting to a null `serde_json::Value`. We still need to update the
Json LSP whenever a new dap is installed.

Release Notes:

- N/A

crates/extension_host/src/wasm_host.rs

@@ -399,7 +399,7 @@ impl extension::Extension for WasmExtension {
         .await
     }
 
-    async fn dap_schema(&self) -> Result<serde_json::Value> {
+    async fn get_dap_schema(&self) -> Result<serde_json::Value> {
         self.call(|extension, store| {
             async move {
                 extension