Support the contentType attribute of the Resource Timing API, and have it and the encoded/decoded body size use the CORS check rather than TAO
Differential Revision: https://phabricator.services.mozilla.com/D208965
bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1800443
gecko-commit: 5b2040f7ddb882e752fd969a7690009574efcd68
gecko-reviewers: sefeng, valentin, webidl, necko-reviewers, saschanaz, emilio