[FIR] Implement checker for exhaustive when's in expression position

compiler/fir/entrypoint/src/org/jetbrains/kotlin/fir/checkers/CommonExpressionCheckers.kt

@@ -28,4 +28,8 @@ object CommonExpressionCheckers : ExpressionCheckers() {
     override val tryExpressionCheckers: Set<FirTryExpressionChecker> = setOf(
         FirCatchParameterChecker
     )
+
+    override val whenExpressionCheckers: Set<FirWhenExpressionChecker> = setOf(
+        FirExhaustiveWhenChecker
+    )
 }