The lack of specificity for script intro type has lead the debugger to need
to make use of 'source.introductionType' and 'source.element' in order to
determine whether a given script was injected, or inline or fetched, which
is entirely unnecessary of the loader itself clearly tells us what type
of script we are working with. It also allows us to cleanly handle the case
of XUL, which previously was "scriptElement" but has no ".element" passed
in, so we were unable to know whether a given source was inline or not.
Differential Revision: https://phabricator.services.mozilla.com/D78435
