Native: fix location offsets in SuspendFunctionN implementations

When generating synthetic Function{N+1}.invoke implementations for
SuspendFunction{N} subclasses, use SYNTHETIC_OFFSET instead of
suspend invoke function location offsets.

This location is more suitable for generated synthetic functions.
Additionally, this fixes the case when suspend invoke is fake override:
fake overrides use UNDEFINED_OFFSET, so the generated function was
getting UNDEFINED_OFFSET as well, leading to incorrect debug
information.

Fix suspendFunctionAsSupertype.kt and suspendFunctionAsSupertypeCall.kt

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/AbstractSuspendFunctionsLowering.kt

@@ -110,8 +110,8 @@ abstract class AbstractSuspendFunctionsLowering<C : CommonBackendContext>(val co
                     clazz.superTypes += functionType
 
                     context.irFactory.buildFun {
-                        startOffset = invokeFunction.startOffset
-                        endOffset = invokeFunction.endOffset
+                        startOffset = SYNTHETIC_OFFSET
+                        endOffset = SYNTHETIC_OFFSET
                         origin = DECLARATION_ORIGIN_COROUTINE_IMPL
                         name = OperatorNameConventions.INVOKE
                         visibility = DescriptorVisibilities.PROTECTED