This changes unreachable code from a warning presented in the editor to an error. Existing issues mostly revolved around switching on enums. These were fixed by converting the switches to use a default case, leaving the behavior unchanged in case of new values (e.g. from separately-compiled extensions) creeping in.

Other cases had to do with the assert.fail() function, which throws and so shouldn't have anything following it.
Co-authored-by: NMaksym Taran <maksym.taran@gmail.com>

Readonly helps with type guards and code comprehension

We compile using the alwaysStrict flag so these directives are not needed

This part removes most `use strict` directives that are right after the file header