dx(runtime-core): add selector in mount warning (#2563)

packages/runtime-dom/src/index.ts

@@ -111,7 +111,9 @@ function normalizeContainer(
   if (isString(container)) {
     const res = document.querySelector(container)
     if (__DEV__ && !res) {
-      warn(`Failed to mount app: mount target selector returned null.`)
+      warn(
+        `Failed to mount app: mount target selector "${container}" returned null.`
+      )
     }
     return res
   }

packages/vue/__tests__/index.spec.ts

@@ -205,7 +205,7 @@ describe('compiler + runtime integration', () => {
     createApp(App).mount('#not-exist-id')
 
     expect(
-      '[Vue warn]: Failed to mount app: mount target selector returned null.'
+      '[Vue warn]: Failed to mount app: mount target selector "#not-exist-id" returned null.'
     ).toHaveBeenWarned()
     document.querySelector = origin
   })