[K/N] Migrate most simple filecheck tests to new infra

^KT-62157


Merge-request: KT-MR-12376
Merged-by: Vladimir Sukharev <Vladimir.Sukharev@jetbrains.com>

compiler/testData/codegen/box/fileCheck/kt49847_generic.kt

@@ -0,0 +1,20 @@
+// TARGET_BACKEND: NATIVE
+// FILECHECK_STAGE: CStubs
+
+class C<T> {
+    fun foo(x: T) = x
+}
+
+// CHECK-LABEL: define %struct.ObjHeader* @"kfun:#box(){}kotlin.String"
+// CHECK-NOT: Int-box
+// CHECK-OPT-NOT: Int-unbox
+// CHECK-DEBUG: Int-unbox
+// CHECK-LABEL: epilogue:
+fun box(): String {
+    val c = C<Int>()
+    val fooref = c::foo
+    return if (fooref(42) == 42)
+        "OK"
+    else
+        "FAIL"
+}