Update Trusted Types content attributes test (#49473)
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Skip attributes that are in WPT IDL but are not implemented in browser IDL.
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Add comment explaining why each set of attributes are included.
encrypted-media event listeners are an interesting case, they're only a TT sink in Firefox currently but as specced they should be in all browsers, so I've kept the tests for them.
See w3c/trusted-types#520 for further discussion on the spec.