MV3 PB fails to block resources initiated by cookieblocked subdomains of the same domain

[ghostwords]

This is the same underlying issue as #3048, just the flip side of it.

For example, if requests to play.google.com are initiated in by a "cookieblocked" google.com subdomain, we will fail to block it with DNR because we set domainType to "thirdParty" and also because we set excludedInitiatorDomains with our MDFP list for Google. Both domainType and excludedInitiatorDomains work with the initiator domain (immediate parent frame's domain, which may or may not be the top-level page domain).

This should be solved by w3c/webextensions#762 and replacement of domainType "thirdParty" with an always present excludedTopDomains entry for the domain itself.