Add support for triple quoted ASCII byte string

[kerams]

Description

Before

> """ " """B;;

  """ " """B;;
  ^^^^^^^^^

stdin(2,1): error FS0003: This value is not a function and cannot be applied.

After

> """ " """B;;
val it: byte array = [|32uy; 34uy; 32uy|]

Didn't bother with a language feature... Also this could TECHNICALLY be breaking if you have something stupid like this in your code today

> let x a b = 7;;
val x: a: 'a -> b: 'b -> int

> let B = ();;
val B: unit = ()

> x """ " """B;;
val it: int = 7

Checklist

• Test cases added
• Performance benchmarks added in case of performance changes
• Release notes entry updated

[kerams]

I'm not sure if it's actually possible to escape triple quotes in a triple quoted string, so this'll have to do.

[Martin521]

This needs a small RFC, please, in the fslang-design repo. To ensure it ends up in the spec.