This change takes all existing WebIDL files in the repo that had
definition lines without four leading spaces, and fixes them so they
have four leading spaces.
(cherry picked from commit 51528ec6779202747cc3b99d3b77772a124a0b47)
This collection has some pretty strange behaviour, particularly with the
IsHTMLDDA slot which is defined in the javascript spec specifically for
this object.
This commit implements pretty much all of this interface, besides from
the custom [[Call]].
There is also no caching over this collection. Since it is a live
collection over the entire document, the performance is never going to
be great, and I am not convinced any speedup for this legacy interface
is worth a massive cache.
