Fixes for KT-4991: Prefix/postfix expressions resolved to local extensions are not supported in codegen;

KT-4989: Verify error on local functions and extensions;
KT-4987: NegativeArraySizeException on local extension convention function on nullable Int

  #KT-4991 Fixed
  #KT-4989 Fixed
  #KT-4987 Fixed

compiler/testData/codegen/box/operatorConventions/kt4987.kt

@@ -0,0 +1,6 @@
+fun box(): String {
+    fun Int?.inc() = (this ?: 0) + 1
+    var counter: Int? = null
+    counter++
+    return if (counter == 1) "OK" else "fail: $counter"
+}

compiler/testData/codegen/box/operatorConventions/kt4991.kt

@@ -0,0 +1,24 @@
+var a = A()
+var b = A()
+
+class A(var value: Int = 0)
+
+fun prefix(inc: A.() -> A)  {
+    ++a
+}
+
+fun postfix(inc: A.() -> A)  {
+    b++
+}
+
+fun box(): String {
+    prefix { ++value; this }
+
+    if (a.value != 1) return "fail 1"
+
+    postfix { value++; this }
+
+    if (b.value != 1) return "fail 2"
+
+    return "OK"
+}