[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/frontend.java/src/org/jetbrains/kotlin/load/java/JavaClassFinderImpl.kt

@@ -52,4 +52,7 @@ class JavaClassFinderImpl : AbstractJavaClassFinder() {
         return javaFacade.knownClassNamesInPackage(packageFqName, javaSearchScope)
     }
 
+    override fun canComputeKnownClassNamesInPackage(): Boolean {
+        return javaFacade.canComputeKnownClassNamesInPackage()
+    }
 }