Textareas have a very weird bug in IE, where the text of the placeholder
is copied to the content of the textarea when set.

This a creates two bugs:
1. An unintended binding is made to the textContent of the textarea's
   text child node, meaning updates to the `placeholder` will be an
   unnecessary binding process in the best case, or an exception thrown
   when updating the text child node in the worst case.
2. When `legacyOptimizations` is enabled, the child node of the text
   area is removed when the binding for `placeholder` is processed and
   removed, leaving a binding to a `null` node, and throwing exceptions.

Therefore, when we detect this placeholder behavior, we will remove the
textnode before template processing, preventing both bugs.