fix(compiler-core): ignore empty siblings between v-if and v-else-if/else

[pikax]

fix #1256

Instead of using at the compiler parsing as in #1262, we ignore the whitespace elements when getting the siblings for vif

https://github.com/vuejs/vue-next/blob/master/packages/compiler-core/src/parse.ts#L203

EDIT:

<div id="app">
	<div />
	<!-- loading -->
	<div />

	Hello
</div>

import { createVNode as _createVNode, createTextVNode as _createTextVNode, openBlock as _openBlock, createBlock as _createBlock } from "vue"

export function render(_ctx, _cache) {
  return (_openBlock(), _createBlock("div", { id: "app" }, [
    _createVNode("div"),
    _createTextVNode(" " + " ", 1 /* TEXT */),
    _createVNode("div"),
    _createTextVNode(" Hello ")
  ]))
}

NOTE

_createTextVNode(" " + " ", 1 /* TEXT */), shouldn't be in the output, for not having it on the output #1262 does the job

[yyx990803]

see f3623e4