IR: fix thisReceiver parameter type for function classes

Incorrect builder was used at line 269, which led to non-sensible type
in `IrClass.thisReceiver` for function types, such as
`SuspendFunction1<SuspendFunction1, SuspendFunction1>` in the linked
issue.

Avoid creating types manually completely to simplify this code and fix
the bug.

 #KT-49168 Fixed

compiler/fir/fir2ir/tests-gen/org/jetbrains/kotlin/test/runners/codegen/FirBlackBoxCodegenTestGenerated.java

@@ -9762,6 +9762,12 @@ public class FirBlackBoxCodegenTestGenerated extends AbstractFirBlackBoxCodegenT
             runTest("compiler/testData/codegen/box/coroutines/kt46813.kt");
         }
 
+        @Test
+        @TestMetadata("kt49168.kt")
+        public void testKt49168() throws Exception {
+            runTest("compiler/testData/codegen/box/coroutines/kt49168.kt");
+        }
+
         @Test
         @TestMetadata("lastExpressionIsLoop.kt")
         public void testLastExpressionIsLoop() throws Exception {