checker: fix incorrect checks when struct fields are ref and option type(fix #19555)

[shove70]

1. Fixed Uncaught type checking error with options and pointers #19555
2. Add tests.

module main
import rand

struct MyType {
	foo string
}

struct TypeWithOption {
	maybe ?&MyType
}

fn main() {
	println("trying...")
	x := rand.int()

	ptr := if x > 0 {
		?MyType(MyType{foo:"bar"})
	} else {
		?MyType(none)
	}

	container := TypeWithOption{maybe: ptr} // Expects ?&MyType, not ?MyType. Sema doesn't catch this, I guess.
	println("success!")
	println(container)
}

outputs:

a.v:22:30: error: cannot assign to field `maybe`: expected a pointer `?&MyType`, but got `?MyType`
   20 |     }
   21 | 
   22 |     container := TypeWithOption{maybe: ptr} // Expects ?&MyType, not ?MyType. Sema doesn't catch this, I guess.
      |                                 ~~~~~~~~~~
   23 |     println("success!")
   24 |     println(container)

[spytheman]

Good work.