[ASTPrinter] Switch to new ParameterTypeFlags
Switch printing off of using Function's ExtInfo for autoclosure and
escaping, and onto the ParameterTypeFlags, which let us do precise and
accurate context-sensitive printing of these parameter type
attributes. This fixes a huge list of issues where we were printing
@escaping for things like optional ObjC completion handlers, among
many others. We now correctly print @escaping in more places, and
don't print it when it's not correct.
Also updates the dumper to be consistent and give a good view of the
AST as represented in memory. Tests updated, more involved testing
coming soon.
