Resolve applied-rule stylesheet identities through StyleSheetsActor and
include Firefox parentStyleSheet, line, and column fields on rule forms.
Firefox can then show matched rules as stylesheet rules and open the
corresponding CSS source location from the Rules panel.
Include parser rule locations and stylesheet identities in the applied
style rule data sent to DevTools. This gives the protocol layer enough
information to map matched rules to existing stylesheet resources
without guessing from displayed rule text.
