Expected type conflation in binop handler

[Simn]

While looking at #11391 I noticed that there's some chaos in operators.ml with regards to with_type. In particular, type_binop2 currently receives only one expected type, but it should really be two: one for the typing of the rhs and one for the typing of the resulting binop.

Will try to construct a failing example.

[Simn]

I don't think there's a failing example here because with_type isn't actually used beyond that point.

Another problem is that we type the lhs of assignments with the expected type of the whole binop. This isn't always correct which can easily be seen at block-level:

function main() {
	var a:Int;
	$type(a, _) = 0;
}

This prints Warning : Int (expected: NoValue), which is wrong because we clearly want a value to assign to.

[Simn]

I'm not even sure if it's technically correct to do this when there is an expected type:

function main() {
	var a:Int;
	var b:Int;
	$type(a, _) = $type(b, _) = 0;
}

source/Main.hx:4: characters 8-9 : Warning : Int (expected: NoValue)
source/Main.hx:4: characters 22-23 : Warning : Int (expected: WithType(Int, None))

While it's true that the result of b = 0 can be expected to be of type Int, that doesn't necessarily mean that b itself can be expected to be of type Int. This is more obvious when we look at it as a = (b = 0).