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/testData/codegen/box/coroutines/kt49168.kt

@@ -0,0 +1,27 @@
+// WITH_RUNTIME
+// WITH_COROUTINES
+// IGNORE_BACKEND: JVM
+// IGNORE_LIGHT_ANALYSIS
+
+import helpers.*
+import kotlin.coroutines.*
+
+fun interface Print {
+    suspend fun print(msg: String): String
+}
+
+object Context : Print by Print(::id)
+
+fun id(x: String): String = x
+
+fun builder(c: suspend () -> Unit) {
+    c.startCoroutine(EmptyContinuation)
+}
+
+fun box(): String {
+    var result = "Fail"
+    builder {
+        result = Context.print("OK")
+    }
+    return result
+}