everywhere: Allow descructuring assignments

[robryanx]

Currently we allow descructuring declarations for example:

let (x, y) = (1, 2)

This extends so that we can do destrucuting assignments for example:

mut x = 0
mut y = 0
(x, y) = (1, 2)

Additionally we can do nested destructuring for example:

mut x = 0
mut y = 0
mut z = 0
(x, (y, z)) = (1, (2, 3))

Will add this for declaration destructuring as part of a separate PR.

Note: This is similar to an older PR: #1161
The main difference being that it specifically only allows Var or JaktTuple for nesting on the LHS. Also the earlier PR had fairly significant parser changes but this version handles it within the typechecker without introducing parsing changes.

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[alimpfard]

Very nice, I'll take a more comprehensive look in a bit but generally looks good.

[alimpfard]

Just one comment!

[alimpfard]

maybe better as an if?

Suggested change

	match expr {
	BinaryOp(lhs, op, rhs) => {
	if op is Assign and lhs is JaktTuple(values) {
	return .typecheck_tuple_assignment(lhs_values: values, rhs, scope_id, safety_mode, span)
	}
	}
	else => {}
	}
	if expr is BinaryOp(lhs, op, rhs) and op is Assign and lhs is JaktTuple(values) {
	return .typecheck_tuple_assignment(lhs_values: values, rhs, scope_id, safety_mode, span)
	}

[robryanx]

Thanks, updated.

[alimpfard]

Thanks!