e892e32df4
Add more tests for the offset_of macro Implements what I [suggested in the tracking issue](https://github.com/rust-lang/rust/issues/106655#issuecomment-1535007205), plus some further improvements: * ensuring that offset_of!(Self, ...) works iff inside an impl block * ensuring that the output type is usize and doesn't coerce. this can be changed in the future, but if it is done, it should be a conscious decision * improving the privacy checking test * ensuring that generics don't let you escape the unsized check r? `````@WaffleLapkin`````