Added test for registerDeclarativeServer

Added test case for registerDeclarativeServer  like we discussed over email

tests/specs/serve/declarativeSer/__test__.jsonc

@@ -0,0 +1 @@
+ 

tests/specs/serve/declarativeSer/server.out

@@ -0,0 +1 @@
+ 

tests/specs/serve/declarativeSer/server.ts

@@ -0,0 +1,3 @@
+export const fetch = (req: Request) => {
+  return new Response("Hello from declarative server!");
+};