This is not really a context, but more of a set of parameters for
creating a Parser. So, treat it as such: Rename it to ParsingParams,
and store its values and methods directly in the Parser instead of
keeping the ParsingContext around.
This has a nice side-effect of not including DOM/Document.h everywhere
that needs a Parser.
Previously, some fuzzers were generating an excessive amount of debug
logging. This change explicitly disables debug logging for all fuzzers.
This allows higher test throughput and makes the logs easier to read
when fuzzing locally.
Instead of trying to create a Window and a Document, and use those to
create a ParsingContext, just use the JS::Realm only constructor to make
sure that bindings are stashed on the main thread VM's realm.
