checkAncestors gives wrong results for BaseAudioContext

[foolip]

In #1300, all members of BaseAudioContext are clamped to the version where the interface is fully supported. This isn't really helpful, since the interface is newer than its members due to things moving around on the prototype chain. BCD uses partial_implementation for this:

https://github.com/mdn/browser-compat-data/blob/8e86a205cfde203fc91f5548c9ffe142ede2270d/api/BaseAudioContext.json#L8-L18

In this case it's Baseline high anyway so it won't matter on MDN, but we may need some way to work around cases like this if it happens on more recent features.