While sanitizing on browsers that don't support the `template` element (pretty much only IE), we create an inert document and we insert content into it via `document.body.innerHTML = unsafeHTML`. The problem is that IE appears to parse the HTML passed to `innerHTML` differently, depending on whether the element has been inserted into a document or not. In particular, it seems to split some strings into multiple text nodes, which would've otherwise been a single node. This ended up throwing off some of the i18n code down the line and causing a handful of failures. I've worked around it by creating a new inert `body` element into which the HTML would be inserted.
PR Close#34305
