Class constants

[Jason2605]

Well detailed description of the change :

This PR adds the ability to define a constant within a class. This comes with the runtime guarantee that the value will not be changed.

E.g

class SomeClass {
    const classVariable = 10; // This will be shared among all "SomeClass" instances

    init() {
        this.x = 10; // "x" is set on the instance
    }
}

print(SomeClass.classVariable); // 10

const x = SomeClass();
const y = SomeClass();

print(x.classVariable); // 10
print(y.classVariable); // 10

SomeClass.classVaraible = 100; // Cannot assign to class constant 'SomeClass.classVariable'.

Resolves: #

#508

Type of change:

• New feature

Housekeeping

• Tests have been updated to reflect the changes done within this PR (if applicable).

• Documentation has been updated to reflect the changes done within this PR (if applicable).

[briandowns]

This looks awesome!

[Jason2605]

Thanks @briandowns!

I was on the fence about this due to the fact that it only provides runtime guarantees (const in a variable(I know that doesn't quite make sense, but hopefully you get what I mean) are detected at compile time).

Probably still worthwhile however