refactor(plugin-legacy): improve default polyfill (#8312)

Author: sapphi-red

packages/plugin-legacy/src/index.ts

@@ -63,12 +63,7 @@ function viteLegacyPlugin(options: Options = {}): Plugin[] {
   const facadeToLegacyPolyfillMap = new Map()
   const facadeToModernPolyfillMap = new Map()
   const modernPolyfills = new Set<string>()
-  // System JS relies on the Promise interface. It needs to be polyfilled for IE 11. (array.iterator is mandatory for supporting Promise.all)
-  const DEFAULT_LEGACY_POLYFILL = [
-    'core-js/modules/es.promise',
-    'core-js/modules/es.array.iterator'
-  ]
-  const legacyPolyfills = new Set(DEFAULT_LEGACY_POLYFILL)
+  const legacyPolyfills = new Set<string>()
 
   if (Array.isArray(options.modernPolyfills)) {
     options.modernPolyfills.forEach((i) => {
@@ -150,11 +145,13 @@ function viteLegacyPlugin(options: Options = {}): Plugin[] {
 
       // legacy bundle
       if (legacyPolyfills.size || genDynamicFallback) {
-        if (!legacyPolyfills.has('es.promise')) {
-          // check if the target needs Promise polyfill because SystemJS relies
-          // on it
-          await detectPolyfills(`Promise.resolve()`, targets, legacyPolyfills)
-        }
+        // check if the target needs Promise polyfill because SystemJS relies on it
+        // https://github.com/systemjs/systemjs#ie11-support
+        await detectPolyfills(
+          `Promise.resolve(); Promise.all();`,
+          targets,
+          legacyPolyfills
+        )
 
         isDebug &&
           console.log(