dyslexicsteak

Deprecate `static mut`

22

Pre-RFC on [IRLO](https://internals.rust-lang.org/t/pre-rfc-deprecate-then-remove-static-mut/20072). [Results](https://www.surveyhero.com/results/1749245/qsry7n7amfk9t2dbanw15vfyo0x06tzj) from research survey to inform discussion with respect to perception of the feature. (JS required) [Rendered](https://github.com/dyslexicsteak/rfcs/blob/master/text/3560-deprecate-static-mut.md)