Test strictly matching `next/dist` packages (#9968)

test/integration/non-next-dist-exclude/app/node_modules/notnext/.gitignore

+!dist

test/integration/non-next-dist-exclude/app/node_modules/notnext/dist/index.js

+const React = require('react')
+
+module.exports = function() {
+  return React.createElement('p', null, 'BrokenExternalMarker')
+}

test/integration/non-next-dist-exclude/app/node_modules/notnext/package.json

+{
+  "name": "notnext",
+  "version": "1.0.0",
+  "main": "dist/index.js",
+  "license": "MIT"
+}

test/integration/non-next-dist-exclude/app/package.json

+{
+  "name": "non-next-dist-exclude",
+  "version": "1.0.0",
+  "main": "index.js",
+  "license": "MIT"
+}

test/integration/non-next-dist-exclude/app/pages/index.js

+import NotNext from 'notnext'
+
+const Page = () => <NotNext />
+
+Page.getInitialProps = () => ({})
+
+export default Page

test/integration/non-next-dist-exclude/test/index.test.js

+/* eslint-env jest */
+/* global jasmine */
+import fs from 'fs-extra'
+import path from 'path'
+import { nextBuild } from 'next-test-utils'
+
+jasmine.DEFAULT_TIMEOUT_INTERVAL = 1000 * 60 * 1
+
+const appDir = path.join(__dirname, '../app')
+let buildId
+
+describe('Non-Next externalization', () => {
+  beforeAll(async () => {
+    await nextBuild(appDir)
+    buildId = await fs.readFile(path.join(appDir, '.next/BUILD_ID'), 'utf8')
+  })
+
+  it('Externalized non-Next dist-using package', async () => {
+    const content = await fs.readFile(
+      path.join(appDir, '.next/server/static', buildId, 'pages/index.js'),
+      'utf8'
+    )
+    expect(content).not.toContain('BrokenExternalMarker')
+  })
+})