JVM_IR: make continuation detection more consistent

* unify various checks for whether a suspend function needs a
    continuation;

  * mark the continuation parameter with an origin (this also allows
    correctly computing the offset of the local in codegen -- see the
    new test);

  * when wrapping `suspend fun main`, use a suspend reference instead of
    a synthetic non-suspend lambda (required to correctly implement the
    previous point, as previously the continuation parameter was passed
    to main() itself correctly only because of very lenient checks in
    AddContinuationLowering).

compiler/tests/org/jetbrains/kotlin/codegen/BlackBoxInlineCodegenTestGenerated.java

@@ -3813,6 +3813,11 @@ public class BlackBoxInlineCodegenTestGenerated extends AbstractBlackBoxInlineCo
             runTestWithPackageReplacement("compiler/testData/codegen/boxInline/suspend/multipleSuspensionPoints.kt", "kotlin.coroutines");
         }
 
+        @TestMetadata("nestedMethodWith2XParameter.kt")
+        public void testNestedMethodWith2XParameter() throws Exception {
+            runTest("compiler/testData/codegen/boxInline/suspend/nestedMethodWith2XParameter.kt");
+        }
+
         @TestMetadata("nonSuspendCrossinline.kt")
         public void testNonSuspendCrossinline_1_2() throws Exception {
             runTestWithPackageReplacement("compiler/testData/codegen/boxInline/suspend/nonSuspendCrossinline.kt", "kotlin.coroutines.experimental");