[FIR] Fix IncDecOperatorsInExpectClass for FIR, add multi-module test

- `IncDecOperatorsInExpectClass.kt` should produce an
  `ACTUAL_WITHOUT_EXPECT` in K2 (see KT-55177). This went unnoticed
  because of KT-55570.
- A similar multi-module test for K1 and K2 has been added, called:
  `multiplatform/incDecOperatorsInExpectClass.kt`.

compiler/testData/diagnostics/tests/multiplatform/incDecOperatorsInExpectClass.kt

@@ -0,0 +1,12 @@
+// FIR_IDENTICAL
+// Issue: KT-49714
+
+// MODULE: common
+// TARGET_PLATFORM: Common
+expect class Counter {
+    operator fun inc(): Counter
+    operator fun dec(): Counter
+}
+
+// MODULE: main()()(common)
+actual typealias Counter = Int

compiler/testData/diagnostics/tests/multiplatform/incDecOperatorsInExpectClass.txt

@@ -0,0 +1,15 @@
+// -- Module: <common> --
+package
+
+public final expect class Counter {
+    public final expect operator fun dec(): Counter
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public final expect operator fun inc(): Counter
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+// -- Module: <main> --
+package
+
+public actual typealias Counter = kotlin.Int