Emit img tags containing unsupported attributes literally.

Previously, we reconstructed the img tag, only including the supported attributes. This meant we removed some attributes, and it also prevented proper escaping of attribute values.

So , for example, this input:

<img src="f.png" alt="hi &quot;there&quot; you" />

would be emitted as:

<img src="f.png" alt="hi "there" you" />

which is invalid because of the repeated quotation marks