Disable running checkers by default (#4644)

* Make checkers be disabled by default

* Allow running checkers in test launcher

kotlin-native/backend.native/tests/runtime/workers/leak_memory_with_worker_termination.kt

@@ -1,7 +1,9 @@
 import kotlin.native.concurrent.*
+import kotlin.native.Platform
 import kotlinx.cinterop.*
 
 fun main() {
+    Platform.isMemoryLeakCheckerActive = true
     val worker = Worker.start()
     // Make sure worker is initialized.
     worker.execute(TransferMode.SAFE, {}, {}).result;

kotlin-native/backend.native/tests/runtime/workers/leak_worker.kt

@@ -1,7 +1,9 @@
 import kotlin.native.concurrent.*
+import kotlin.native.Platform
 import kotlinx.cinterop.*
 
 fun main() {
+    Platform.isMemoryLeakCheckerActive = true
     val worker = Worker.start()
     // Make sure worker is initialized.
     worker.execute(TransferMode.SAFE, {}, {}).result;

kotlin-native/backend.native/tests/runtime/workers/worker_threadlocal_no_leak.kt

@@ -4,11 +4,13 @@
  */
 
 import kotlin.native.concurrent.*
+import kotlin.native.Platform
 
 @ThreadLocal
 var x = Any()
 
 fun main() {
+    Platform.isMemoryLeakCheckerActive = true
     val worker = Worker.start()
 
     worker.execute(TransferMode.SAFE, {}) {