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/javac-wrapper/src/org/jetbrains/kotlin/javac/components/JavacBasedClassFinder.kt

@@ -21,6 +21,7 @@ import org.jetbrains.kotlin.config.LanguageVersionSettings
 import org.jetbrains.kotlin.javac.JavacWrapper
 import org.jetbrains.kotlin.load.java.AbstractJavaClassFinder
 import org.jetbrains.kotlin.load.java.JavaClassFinder
+import org.jetbrains.kotlin.load.java.structure.JavaClass
 import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.resolve.BindingTrace
 import org.jetbrains.kotlin.resolve.lazy.KotlinCodeAnalyzer
@@ -42,6 +43,8 @@ class JavacBasedClassFinder : AbstractJavaClassFinder() {
         // TODO: reuse previouslyFoundClassFileContent if it's possible in javac
         javac.findClass(request.classId, javaSearchScope)
 
+    override fun findClasses(request: JavaClassFinder.Request): List<JavaClass> = listOfNotNull(findClass(request))
+
     override fun findPackage(fqName: FqName, mayHaveAnnotations: Boolean) = javac.findPackage(fqName, javaSearchScope)
 
     override fun knownClassNamesInPackage(packageFqName: FqName) = javac.knownClassNamesInPackage(packageFqName)