[FIR] Rename new visibilities to CamelCase

It's more convenient since they are objects now instead of
  const fields in FE 1.0

compiler/fir/dump/src/org/jetbrains/kotlin/fir/dump/HtmlFirDump.kt

@@ -521,7 +521,7 @@ class HtmlFirDump internal constructor(private var linkResolver: FirLinkResolver
     }
 
     private fun FlowContent.visibility(visibility: Visibility) {
-        if (visibility == Visibilities.UNKNOWN)
+        if (visibility == Visibilities.Unknown)
             return unresolved { keyword("public?") }
         return keyword(visibility.toString())
     }