checker: fixes cast comparison between generics

This PR introduce the error in the cast comparison when generics are used.

This is an example of stacktrace

```
➜  v git:(macros/generic_cast) ✗ ./v vlib/v/checker/tests/generic_cast_complex_interface.vv
vlib/v/checker/tests/generic_cast_complex_interface.vv:29:10: error: cannot cast `Some<ParseRes>` to `Token, ParseErr>`
   27 |     match r {
   28 |         Some<ParseRes> {
   29 |             rx := Result<[]Token, ParseErr>(r)
      |                   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   30 |             println(rx)
   31 |         }
```

Signed-off-by: Vincenzo Palazzo <vincenzopalazzodev@gmail.com>

vlib/v/checker/tests/generic_cast_complex_interface.vv

@@ -0,0 +1,34 @@
+type ParseRes = Result<[]Token, ParseErr>
+
+struct ParseErr{
+
+}
+
+type Opt<T> = None<T> | Some<T>
+
+struct None<T> {}
+
+struct Some<T> {
+	value T
+}
+
+type Result<T, U> = Err<U> | Ok<T>
+
+struct Ok<T> {
+	value T
+}
+
+struct Err<U> {
+	value U
+}
+
+fn main() {
+	r := Opt<ParseRes>(None<ParseRes>{})
+	match r {
+		Some<ParseRes> {
+			rx := Result<[]Token, ParseErr>(r)
+			println(rx)
+		}
+		None<ParseRes> {}
+	}
+}