checker: missing string/bool invalid operation validation as concrete type

[felipensp]

Fix #18007 (first issue)

struct Wrapped[T] {
	value T
}

fn (w Wrapped[T]) double() Wrapped[T] {
	return Wrapped[T]{w.value * 2}
}

fn make_wrapped[T](value T) Wrapped[T] {
	return Wrapped[T]{value}
}

fn main() {
	println(make_wrapped('str'))
}