refactor(runtime-core): extract promise check into shared (#325)

packages/shared/src/index.ts

@@ -41,6 +41,10 @@ export const isSymbol = (val: any): val is symbol => typeof val === 'symbol'
 export const isObject = (val: any): val is Record<any, any> =>
   val !== null && typeof val === 'object'
 
+export function isPromise<T = any>(val: any): val is Promise<T> {
+  return isObject(val) && isFunction(val.then) && isFunction(val.catch)
+}
+
 export const objectToString = Object.prototype.toString
 export const toTypeString = (value: unknown): string =>
   objectToString.call(value)