Enforce ALL_CAPS variables to be declared as const

[aicioara]

ALL_CAPS variables, by convention are constants. It would be nice to have a rule that enforces const instead of let for those.

This might not be needed if #491 is active, but I prefer this weaker form.

[JoshuaKGoldberg]

I would argue that this complements prefer-const quite nicely. Together, they enforce that any variable in UPPER_CASE must be const and therefore never modified.

[reduckted]

Check out tslint-consistent-codestyle and the naming-convention rule. It's very flexible and you should be able to get the outcome that you're after.

The only thing is that it sort of works in the opposite direction to what you wanted. Instead of enforcing const for uppercase variable names, it would enforce uppercase variable names for const variables.

[adidahiya]

fixed by #2936