fix(hydration): vnode is of Text type and with empty text should be skipped when hydrateChildren

[HcySunYang]

Fix: #3245

[HcySunYang]

When a component just renders an empty string:

const Comp = { render: () => '' }

the ssr result is: nothing

the client rendering result is: Text Node

This causes hydration failure, it can be reproduced with the test case shown below:

  test('empty string', async () => {
    const Comp = { render: () => '' }
    // hydration failure
    mountWithHydration('<div></div>', () =>
      h('div', h(Comp))
    )
  })

This PR did not solve the above problem