refactor: move prop decorator into core, expose initial props to initialziers

packages/runtime-core/src/optional/propDecorator.ts

@@ -0,0 +1,24 @@
+import { Component } from '../component'
+import { PropValidator } from '../componentOptions'
+import { camelize } from '@vue/shared'
+
+export function prop(
+  target: Component | PropValidator<any>,
+  key?: string
+): any {
+  if (key) {
+    applyProp(target, key)
+  } else {
+    const options = target as PropValidator<any>
+    return (target: any, key: string) => {
+      applyProp(target, key, options)
+    }
+  }
+}
+
+function applyProp(target: any, key: string, options: PropValidator<any> = {}) {
+  // here `target` is the prototype of the component class
+  Object.defineProperty(target, `__prop_${camelize(key)}`, {
+    value: options
+  })
+}