[K/N] Move special backend checks test sources to diagnostic tests folder

^KT-61564

compiler/testData/diagnostics/nativeTests/specialBackendChecks/nativeRef/t52.kt

@@ -0,0 +1,6 @@
+import kotlin.native.ref.*
+
+@OptIn(kotlin.experimental.ExperimentalNativeApi::class)
+fun foo(x: Int) {
+    createCleaner(42) { println(x) }
+}

compiler/testData/diagnostics/nativeTests/specialBackendChecks/nativeRef/t53.kt

@@ -0,0 +1,10 @@
+import kotlin.native.ref.*
+
+class C(val x: Int) {
+    fun bar(y: Int) = println(x + y)
+}
+
+@OptIn(kotlin.experimental.ExperimentalNativeApi::class)
+fun foo(x: Int) {
+    createCleaner(42, C(x)::bar)
+}