Disable running checkers by default (#4644)

* Make checkers be disabled by default

* Allow running checkers in test launcher

kotlin-native/backend.native/tests/interop/objc_with_initializer/objc_test.kt

@@ -1,7 +1,9 @@
 import objc_misc.*
+import kotlin.native.Platform
 
 val a = B.giveC()!! as C
 
 fun main() {
+  Platform.isMemoryLeakCheckerActive = true
   println("OK")
-}
+}