[FIR] Add INAPPLICABLE_OPERATOR_MODIFIER diagnostic

compiler/testData/diagnostics/tests/operatorsOverloading/compareToNullable.fir.kt

@@ -1,7 +1,7 @@
 // !DIAGNOSTICS: -UNUSED_PARAMETER
 
 class C {
-    operator fun compareTo(c: C): Int? = null
+    <!INAPPLICABLE_OPERATOR_MODIFIER!>operator<!> fun compareTo(c: C): Int? = null
 }
 
 fun test(c: C) {
@@ -9,4 +9,4 @@ fun test(c: C) {
     c <= c
     c >= c
     c > c
-}
+}

compiler/testData/diagnostics/tests/operatorsOverloading/kt1028.fir.kt

@@ -1,35 +0,0 @@
-//KT-1028 Wrong type checking for plusAssign
-package kt1028
-
-import java.util.*
-
-class event<T>()
-{
-    val callbacks = ArrayList< Function1<T, Unit> >() // Should be ArrayList<()->Unit>, bug posted
-
-    operator fun plusAssign(f : (T) -> Unit) = callbacks.add(f)
-    operator fun minusAssign(f : (T) -> Unit) = callbacks.remove(f)
-    fun call(value : T) { for(c in callbacks) c(value) }
-}
-
-class MouseMovedEventArgs()
-{
-    public val X : Int = 0
-}
-
-class Control()
-{
-    public val MouseMoved : event<MouseMovedEventArgs> = event<MouseMovedEventArgs>()
-
-    fun MoveMouse() = MouseMoved.call(MouseMovedEventArgs())
-}
-
-class Test()
-{
-    fun test()
-    {
-        val control = Control()
-        control.MouseMoved <!ASSIGNMENT_OPERATOR_SHOULD_RETURN_UNIT!>+=<!> { it.X } // here
-        control.MouseMoved.plusAssign( { it.X } ) // ok
-    }
-}

compiler/testData/diagnostics/tests/operatorsOverloading/kt1028.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 //KT-1028 Wrong type checking for plusAssign
 package kt1028