fix(plugin-legacy): polyfill latest features (#7514)

Author: sapphi-red

packages/playground/legacy/__tests__/legacy.spec.ts

@@ -83,4 +83,8 @@ if (isBuild) {
   test('should emit css file', async () => {
     expect(listAssets().some((filename) => filename.endsWith('.css')))
   })
+
+  test('includes structuredClone polyfill which is supported after core-js v3', () => {
+    expect(findAssetFile(/polyfills-legacy/)).toMatch('"structuredClone"')
+  })
 }

packages/playground/legacy/index.html

@@ -1,6 +1,7 @@
 <h1 id="app"></h1>
 <div id="env"></div>
 <div id="iterators"></div>
+<div id="features-after-corejs-3"></div>
 <div id="babel-helpers"></div>
 <div id="assets"></div>
 <script type="module" src="./main.js"></script>

packages/playground/legacy/main.js

@@ -21,6 +21,12 @@ text('#env', `is legacy: ${isLegacy}`)
 // Iterators
 text('#iterators', [...new Set(['hello'])].join(''))
 
+// structuredClone is supported core.js v3.20.0+
+text(
+  '#features-after-corejs-3',
+  JSON.stringify(structuredClone({ foo: 'foo' }))
+)
+
 // babel-helpers
 // Using `String.raw` to inject `@babel/plugin-transform-template-literals`
 // helpers.

packages/plugin-legacy/index.js

@@ -330,7 +330,10 @@ function viteLegacyPlugin(options = {}) {
               loose: false,
               useBuiltIns: needPolyfills ? 'usage' : false,
               corejs: needPolyfills
-                ? { version: 3, proposals: false }
+                ? {
+                    version: require('core-js/package.json').version,
+                    proposals: false
+                  }
                 : undefined,
               shippedProposals: true,
               ignoreBrowserslistConfig: options.ignoreBrowserslistConfig