[Typecheck] Redundant check of invalid type annotation

[aosen-xiong]

In type check, the inivalid type annotation should all be checked validator. However, the visitor also check for invalid annotation at https://github.com/Ao-senXiong/immutability/blob/07f7ee903d48d08c034b522b14feb680c1195cc5/src/main/java/pico/typecheck/PICONoInitVisitor.java#L391. Think about how to unify them and move to validator.

Why? Because there are redundant error messages that might cause confusion.

[aosen-xiong]

Unified the conflict annotation check in aosen-xiong@4eae21e.

One corner case is, there is currently no error at first A a4.

public class ConflictAnnotationTest {
    @Mutable class A {}
    @Immutable class B {}
    @ReceiverDependentMutable class C {}
    class MutableClass {
        @ReceiverDependentMutable A a4;
        @ReceiverDependentMutable B b4;
    }

    @Immutable class ImmutableClass {
        @ReceiverDependentMutable A a4;
        @ReceiverDependentMutable B b4;
    }

    @ReceiverDependentMutable class ReceiverDependentMutableClass {
        @ReceiverDependentMutable A a4;
        @ReceiverDependentMutable B b4;
    }
}