Add constant variables to E2

[Vurv78]

Allows creating immutable variables with const keyword.

Brings the language a little closer to typescript and a lot of people may just prefer this over lua's odd local keyword.

const X = 5

const X = 2 # Compile error
local X = 2 # Compile error
X = 2 # Compile error

print(X)

Potentially inputs could be marked as const with this too (since mutating them does nothing)

Also prevents you from redeclaring local variables in a scope, which is allowed for backwards compat

local X = 5
local X = 5 # Allowed, albeit with a warning now

const X = 5
const X = 5 # Compile error

[Fasteroid]

yes please~

[Denneisk]

I see AOT optimization in your future.

[Vurv78]

Nah this is more of a cosmetic change if anything, I could very well just treat local X = 5 the same as const X = 5 assuming it's never mutated.

Thinking of adding let too but that's not really necessary right now. At least const adds something in that you can be sure a variable is never mutated

[Fasteroid]

Nah this is more of a cosmetic change if anything

balls, so no const @persist?