[FIR] KT-57207 Avoid FirJavaFacade.knownClassNamesInPackage in the IDE

- `FirJavaFacade.knownClassNamesInPackage` cannot be computed in the IDE
  using the current strategy because there are multiple finders and
  there is no `CliFinder`. However, the cache was still used, which
  caused it to be filled with `null` values and additionally caused
  worse performance in `JavaSymbolProvider` due to hash map accesses via
  `hasTopLevelClassOf`.
- Rewriting the strategy is non-trivial as additional indices are needed
  on the IDE side. See KTIJ-24642.

compiler/resolution.common.jvm/src/org/jetbrains/kotlin/resolve/jvm/KotlinJavaPsiFacade.java

@@ -220,13 +220,18 @@ public class KotlinJavaPsiFacade implements Disposable {
 
         KotlinPsiElementFinderWrapper[] finders = finders();
 
-        if (finders.length == 1 && finders[0] instanceof CliFinder) {
+        if (canComputeKnownClassNamesInPackage()) {
             return ((CliFinder) finders[0]).knownClassNamesInPackage(packageFqName);
         }
 
         return null;
     }
 
+    public Boolean canComputeKnownClassNamesInPackage() {
+        KotlinPsiElementFinderWrapper[] finders = finders();
+        return finders.length == 1 && finders[0] instanceof CliFinder;
+    }
+
     @NotNull
     private PsiClass[] findClassesInDumbMode(@NotNull String qualifiedName, @NotNull GlobalSearchScope scope) {
         String packageName = StringUtil.getPackageName(qualifiedName);