feat(compiler-core): remove repeat key

[soouup]

Remove the repeat key in v-if when you set key property directly.

Template:

<div>
  <div v-if="xxx" key="2"></div>
</div>

Before:

import { openBlock, createVNode, createBlock, createCommentVNode } from "vue"

export function render() {
  const _ctx = this
  return (openBlock(), createBlock("div", null, [
    (openBlock(), (_ctx.xxx)
      ? createBlock("div", {
          // this key is redundant
          key: 0,
          key: "2"
        })
      : createCommentVNode("v-if", true))
  ]))
}

After:

import { openBlock, createVNode, createBlock, createCommentVNode } from "vue"

export function render() {
  const _ctx = this
  return (openBlock(), createBlock("div", null, [
    (openBlock(), (_ctx.xxx)
      ? createBlock("div", { key: "2" })
      : createCommentVNode("v-if", true))
  ]))
}

[yyx990803]

Can you add a test case for this? Can be in vIf.spec.ts and simply assert the snapshot.