Extend @vitejs/plugin-legacy

Add option modernTargets to @vitejs/plugin-legacy before official support:

• vitejs/vite#14527
• vitejs/vite#6922
• vitejs/vite#10093

legacy({
  targets: ['chrome 87', 'safari 13', 'firefox 78', 'edge 88'],
  // use modernTargets
  modernPolyfills: true,
  modernTargets: [
    'defaults',
    'chrome 87',
    'safari 13',
    'firefox 78',
    'edge 88'
  ]
})