Implement makeNullableAsSpecified for TypeTemplate properly

This change fixes an SOE in isCastErased:
    @JvmStatic
    fun isCastErased(supertype: KotlinType, subtype: KotlinType, typeChecker: KotlinTypeChecker): Boolean {
        if (supertype.isMarkedNullable || subtype.isMarkedNullable) {
            return isCastErased(TypeUtils.makeNotNullable(supertype), TypeUtils.makeNotNullable(subtype), typeChecker)
        }

TypeUtils.makeNotNullable(TypeTemplate) should not return the same object
if isMarkedNullable returned true on the instance


 #KT-15516 Fixed

compiler/testData/diagnostics/testsWithStdLib/coroutines/inference/kt15516.kt

@@ -0,0 +1,18 @@
+// SKIP_TXT
+class StateMachine<Q> internal constructor() {
+    fun getInputStub(): Q = null as Q
+}
+
+fun <T> stateMachine(<!UNUSED_PARAMETER!>block<!>: suspend StateMachine<T>.() -> Unit): StateMachine<T> {
+    return StateMachine<T>()
+}
+
+class Problem<F>(){
+    fun getInputStub(): F = null as F
+
+    fun createStateMachine(): StateMachine<F> = stateMachine {
+        val letter = getInputStub()
+        if (letter is Any)
+            println("yes")
+    }
+}