Add tests for iframe, textarea

[arobase-che]

Hi,

I would like to add to add 2 tests to highlight an old bug. (I met it twice in two different contexts)

The TAP Result :

    operator: deepEqual
    expected: |-
      { data: { quirksMode: false }, type: 'root', children: [ { type: 'element', tagName: 'textarea', properties: {}, children: [ { type: 'text', value: 'Some text' } ] }, { type: 'element', tagName: 'img', properties: { alt: 'foo', src: 'bar.jpg' }, children: [] } ] }
    actual: |-
      { type: 'root', children: [ { type: 'element', tagName: 'textarea', properties: {}, children: [ { type: 'text', value: 'Some text' } ] }, { type: 'text', value: '<img alt="foo" src="bar.jpg">' } ], data: { quirksMode: false } }

We can see that a raw node is interpreted as text : { type: 'text', value: '<img alt="foo" src="bar.jpg">' }

This is caused by the fact that the parser of parse5 switch the state of the tokenizer to RCDATA (interpret everything as text i suppose) inside a iframe or textarea but i doesn't put it back to his normal state.

In fact, the tokenizer should manage his own state as it does with parse5 but it doesn't here. I think it's because hast-util-raw use internal function of parser5.

^^