feat(compiler)!: Partial function application

[alex-snezhko]

Partial function application

let add = (x, y) => x + y
let add1 = partial add(1, _)
assert add1(2) == 3

let printValues = (x, y, z=3) => {
  print(x)
  print(y)
  print(z)
}
let printSome = partial printValues(y=2, _, z=_)
printSome(1) // prints 1, 2, 3

Closes #402

[alex-snezhko]

TODO:

• Make precedence of partial tighter to allow x |> partial add(_, y) without parentheses around the partial expression
• Decide if this feature should be supported for infix functions - doesn't seem particularly useful so will not do in this PR

[alex-snezhko]

This was kind of a bandaid fix around me being a noob with LR(1) parsers and not being able to figure out how to create separate rules for partial and total applications without reduce/reduce conflicts. If anyone has insight on how to do this please let me know

[ospencer]

Marked this as breaking because of the new keywords.