* Add unmeasurable variance kind for marking types whose variance result is unreliable
* Remove now-unneeded nongeneric checks
* Add rule allowing `Readonly<any>` to be `any` instead of `{readonly [index: string]: any}`
* All Unmeasurable variances to still shortcut structural comparisons in some cases
* Separate unmeasurable from unreliable to reduce the impact of this change, for now
* Fix lint
* Remove Readonly<any> -> any callout
* Add fix for circularity error triggered by deep signature return type comparisons with `this` types
