FIR: implement checker for open members

Specifically,

1. NON_FINAL_MEMBER_IN_FINAL_CLASS
2. NON_FINAL_MEMBER_IN_OBJECT

compiler/testData/diagnostics/tests/override/overrideMemberFromFinalClass.fir.kt

@@ -1,5 +1,5 @@
 class Foo {
-    open fun openFoo() {}
+    <!NON_FINAL_MEMBER_IN_FINAL_CLASS!>open<!> fun openFoo() {}
     fun finalFoo() {}
 }
 
@@ -25,4 +25,4 @@ abstract class A2 {
 class B2 : A2()
 class C2 : B2() {
     override fun foo() {}
-}
+}