Retain typed generics in ObjC export stubs (#4727)

* Add ObjC export test with disabled generics
* Retain typed generics in ObjC export stubs
* Introduce ObjC variance enum to decouple stubs from Kotlin variance

(cherry picked from commit 4d7c78b952a467ca3318c8c49d36b768fdc1ef9c)

kotlin-native/build-tools/src/main/kotlin/org/jetbrains/kotlin/FrameworkTest.kt

@@ -30,6 +30,9 @@ open class FrameworkTest : DefaultTask(), KonanTestExecutable {
     @Input
     lateinit var swiftSources: List<String>
 
+    @Input
+    var swiftExtraOpts: List<String> = emptyList()
+
     @Input
     lateinit var frameworks: MutableList<Framework>
 
@@ -159,7 +162,7 @@ open class FrameworkTest : DefaultTask(), KonanTestExecutable {
                 "-F", frameworkParentDirPath,
                 "-Xcc", "-Werror" // To fail compilation on warnings in framework header.
         )
-        compileSwift(project, project.testTarget, sources, options, Paths.get(executable), fullBitcode)
+        compileSwift(project, project.testTarget, sources, options + swiftExtraOpts, Paths.get(executable), fullBitcode)
     }
 
     @TaskAction