[code_review] Rewrite interface definitions to their actual implementation using Searchfox API

As suggested by @asutherland:

for stuff like this manual expansion of nsIWidget's subclasses that says searchfox doesn't have the functionality, searchfox does have that data. inheritance-diagram:'nsIWidget' depth:4 is a nice demonstration of this (attaching screnshot too). But it's also exposed like in id:nsiwidget under the "Subclasses". But also all the semantic data is directly available via the "sorch" endpoint; also, the results data is raw rather than the pre-chewing for presentation purposes that the "search" endpoint does that makes it an awkward programmatic endpoint. (Search in the searchfox CMO channel for "sorch" for more.)