…the duality that the value can be set in either the child node, or in the value _parameter_ (not attribute)

 - this is to fix up 'historical' recordings, as duplicate textarea content should no longer be being created at record time (see previous commit in this PR)
 - new test shows what the snapshot generated by previous versions of rrweb used to look like, hence 'bad'
 - original 0efe23f fix either didn't work or no longer works due to childNodes being appended subsequent to this part of the code

…he value was recorded as a child node

 - I didn't notice that form.html was used in other tests, so lucky that I noticed that those tests also should have the 'pre value' masked out

…build

…te (from it's DOM property) and not as a childNode. It should still be rebuilt as a childNode rather than a property

…e was extremely painful to get right from a typings point of view)

…prehension of why we are doing things this way