fix(compiler-core): should attach key into fragment if `<template v-f…

[underfin]

…or/>` has normal children

fix #1907

[underfin]

It will be hosited key props.I'm try add code to resolve it ...
<template v-for="item in items" :key="item"><span/></template> will be compiled

const _Vue = Vue
const { createVNode: _createVNode } = _Vue

const _hoisted_1 = { key: item }

return function render(_ctx, _cache, $props, $setup, $data, $options) {
  with (_ctx) {
    const { renderList: _renderList, Fragment: _Fragment, openBlock: _openBlock, createBlock: _createBlock, createVNode: _createVNode } = _Vue

    return (_openBlock(true), _createBlock(_Fragment, null, _renderList(items, (item) => {
      return (_openBlock(), _createBlock("span", _hoisted_1))
    }), 128 /* KEYED_FRAGMENT */))
  }
}

// Check the console for the AST