[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.

core/descriptors.runtime/src/org/jetbrains/kotlin/descriptors/runtime/components/ReflectJavaClassFinder.kt

@@ -42,6 +42,7 @@ class ReflectJavaClassFinder(private val classLoader: ClassLoader) : JavaClassFi
     }
 
     override fun knownClassNamesInPackage(packageFqName: FqName): Set<String>? = null
+    override fun canComputeKnownClassNamesInPackage(): Boolean = false
 }
 
 fun ClassLoader.tryLoadClass(fqName: String) =