feat: Support getComputedStyle API

[devjiangzhou]

#80

TODO:

• valueForPropertyInStyle
  • Font
  • Margin
  • Padding
  • Background
  • Border
  • Text
  • Animation
• Test Spec
  • background
  • Font
  • Border
• JS API

---

vant:
transition-property
transition-delay
transition-duration
animation-delay
animation-duration

[suyulin]

vant-picker need transform

function getElementTranslateY(element: Element) {
  const { transform } = window.getComputedStyle(element);
  const translateY = transform.slice(7, transform.length - 1).split(', ')[5];
  return Number(translateY);
}