fix(types): properly infer return type from async setup (#2051)

fix #2049

test-dts/defineComponent.test-d.tsx

@@ -864,3 +864,39 @@ describe('extract instance type', () => {
   //  @ts-expect-error
   expectError((compA.baseA = 1))
 })
+
+describe('async setup', () => {
+  type GT = string & { __brand: unknown }
+  const Comp = defineComponent({
+    async setup() {
+      // setup context
+      return {
+        a: ref(1),
+        b: {
+          c: ref('hi')
+        },
+        d: reactive({
+          e: ref('hello' as GT)
+        })
+      }
+    },
+    render() {
+      // assert setup context unwrapping
+      expectType<number>(this.a)
+      expectType<string>(this.b.c.value)
+      expectType<GT>(this.d.e)
+
+      // setup context properties should be mutable
+      this.a = 2
+    }
+  })
+
+  const vm = {} as InstanceType<typeof Comp>
+  // assert setup context unwrapping
+  expectType<number>(vm.a)
+  expectType<string>(vm.b.c.value)
+  expectType<GT>(vm.d.e)
+
+  // setup context properties should be mutable
+  vm.a = 2
+})