FIR IDE: Add visibility checks to the completion

Visibility checks currently do not work in some cases, for example:

- public nested class of private class is seen globally
- private_for_this does not work
- some other cases I am not yet aware of

If `FirVisibilityChecker.isVisible` fix those issues, they will be fixed
automatically in the completion

idea/idea-completion/testData/basic/multifile/NotImportedFunction/NotImportedFunction.dependency.kt

@@ -6,3 +6,5 @@ fun globalFun2(): Int = 1
 object Some {
     fun globalFun3(): Int = 3
 }
+
+private fun globalFunPrivate() {}

idea/idea-completion/testData/basic/multifile/NotImportedFunction/NotImportedFunction.kt

@@ -7,3 +7,4 @@ fun testFun() {
 
 // EXIST: globalFun1, globalFun2
 // ABSENT: globalFun3
+// ABSENT: globalFunPrivate