Bug 1539948, part 3 - Only allow nostdcall methods and attributes on...

Bug 1539948, part 3 - Only allow nostdcall methods and attributes on builtinclass interfaces. r=nika

We don't properly implement them in JS, so only allow them for C++.

This patch also makes the only remaining non-builtinclass interface
with a nostdcall method, nsIBinaryOutputStream, builtinclass.

This also changes the isScriptable() method to be consistent,
though I think the change doesn't matter because the only
place that calls it also checks if the interface is builtinclass.

Differential Revision: https://phabricator.services.mozilla.com/D98863