feat(types): feat(types): add ComponentCustomProperties interface (#982)

test-dts/componentCustomProperties.test-d.ts

@@ -0,0 +1,20 @@
+import { expectError } from 'tsd'
+import { defineComponent } from './index'
+
+declare module '@vue/runtime-core' {
+  interface ComponentCustomProperties {
+    state: 'stopped' | 'running'
+  }
+}
+
+export const Custom = defineComponent({
+  data: () => ({ counter: 0 }),
+  methods: {
+    aMethod() {
+      expectError(this.notExisting)
+      this.counter++
+      this.state = 'running'
+      expectError((this.state = 'not valid'))
+    }
+  }
+})