KT-57207 Implement JavaClassFinder.findClasses

- This change is a prerequisite for allowing combined Java symbol
  providers (in LL FIR) to correctly disambiguate classpath order after
  getting classes with a combined scope, as the index access of the
  combined Java symbol provider is not guaranteed to return the class
  that should be first based on the original dependency order. To be
  able to disambiguate, a combined Java symbol provider needs access to
  all class candidates the index can find.

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

@@ -44,6 +44,10 @@ class JavaClassFinderImpl : AbstractJavaClassFinder() {
         return javaFacade.findClass(request, javaSearchScope)
     }
 
+    override fun findClasses(request: JavaClassFinder.Request): List<JavaClass> {
+        return javaFacade.findClasses(request, javaSearchScope)
+    }
+
     override fun findPackage(fqName: FqName, mayHaveAnnotations: Boolean): JavaPackage? {
         return javaFacade.findPackage(fqName.asString(), javaSearchScope)?.let { JavaPackageImpl(it, javaSearchScope, mayHaveAnnotations) }
     }