[ObjCType] Add basic implementation of base method, fix tests

KT-65687

native/objcexport-header-generator/testData/headers/superClassWithCovariantOverride/!superClassWithCovariantOverride.h

@@ -0,0 +1,38 @@
+#import <Foundation/NSArray.h>
+#import <Foundation/NSDictionary.h>
+#import <Foundation/NSError.h>
+#import <Foundation/NSObject.h>
+#import <Foundation/NSSet.h>
+#import <Foundation/NSString.h>
+#import <Foundation/NSValue.h>
+
+@class Bar;
+
+NS_ASSUME_NONNULL_BEGIN
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wunknown-warning-option"
+#pragma clang diagnostic ignored "-Wincompatible-property-type"
+#pragma clang diagnostic ignored "-Wnullability"
+
+#pragma push_macro("_Nullable_result")
+#if !__has_feature(nullability_nullable_result)
+#undef _Nullable_result
+#define _Nullable_result _Nullable
+#endif
+
+@interface Bar : Base
+- (instancetype)init __attribute__((swift_name("init()"))) __attribute__((objc_designated_initializer));
++ (instancetype)new __attribute__((availability(swift, unavailable, message="use object initializers instead")));
+- (id)foo __attribute__((swift_name("foo()")));
+@end
+
+__attribute__((objc_subclassing_restricted))
+@interface Foo : Bar
+- (instancetype)init __attribute__((swift_name("init()"))) __attribute__((objc_designated_initializer));
++ (instancetype)new __attribute__((availability(swift, unavailable, message="use object initializers instead")));
+- (NSString *)foo __attribute__((swift_name("foo()")));
+@end
+
+#pragma pop_macro("_Nullable_result")
+#pragma clang diagnostic pop
+NS_ASSUME_NONNULL_END

native/objcexport-header-generator/testData/headers/superClassWithCovariantOverride/Foo.kt

@@ -0,0 +1,7 @@
+abstract class Bar {
+    abstract fun foo(): Any
+}
+
+class Foo : Bar() {
+    override fun foo(): String = error("stub")
+}