Fix accessor generation for suspend functions

1. JVM view of suspend accessors must be also an instance of AccessorForFunctionDescriptor,
thus `createSubstitutedCopy` should be correctly overidden.

2. accessibleFunctionDescriptor should unwap the initial suspend descriptor,
for the same reasons as for type aliases constructors and etc:
these descriptors are used as keys of the map of accessors, so
to avoid duplication for suspend view and initial suspend descriptor,
we always use the latter one as a key.

 #KT-15907 Fixed
 #KT-15935 Fixed

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

@@ -5179,6 +5179,18 @@ public class LightAnalysisModeCodegenTestGenerated extends AbstractLightAnalysis
                 doTest(fileName);
             }
 
+            @TestMetadata("privateFunctions.kt")
+            public void testPrivateFunctions() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/coroutines/suspendFunctionAsCoroutine/privateFunctions.kt");
+                doTest(fileName);
+            }
+
+            @TestMetadata("privateInFile.kt")
+            public void testPrivateInFile() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/coroutines/suspendFunctionAsCoroutine/privateInFile.kt");
+                doTest(fileName);
+            }
+
             @TestMetadata("returnNoSuspend.kt")
             public void testReturnNoSuspend() throws Exception {
                 String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/coroutines/suspendFunctionAsCoroutine/returnNoSuspend.kt");