This replaces the JS policy service stubs with a pure C++ version which
directly makes policy decisions based on active WebExtensionPolicy objects.
This is the first step in a larger refactoring, which will remove the
ExtensionManagement module entirely, and replace the current add-on policy
service with direct, non-virtual access to native WebExtensionPolicy objects.
It will also be followed by related changes to migrate the content script and
extension page matching to native code, based on the existing MatchPattern and
WebExtensionPolicy bindings.
MozReview-Commit-ID: 2MpbmXZGiPZ
e5aca6859e