Replace JavaClass.innerClasses with innerClassNames

Also add a findInnerClass method that can find an inner class
by its name

This change helps to avoid loading all the inner class files
eagerly (that may be rather slow), while all the names are available
in InnerClass attribute

core/descriptors.runtime/src/org/jetbrains/kotlin/load/java/structure/reflect/ReflectJavaClass.kt

@@ -31,7 +31,7 @@ class ReflectJavaClass(
 
     override val modifiers: Int get() = klass.modifiers
 
-    override val innerClasses: List<ReflectJavaClass>
+    override val innerClassNames: List<Name>
         get() = klass.declaredClasses
                 .asSequence()
                 .filterNot {
@@ -40,8 +40,13 @@ class ReflectJavaClass(
                     // nested class constructor accessed from the outer class
                     it.simpleName.isEmpty()
                 }
-                .map(::ReflectJavaClass)
-                .toList()
+                .mapNotNull { it.simpleName.takeIf(Name::isValidIdentifier)?.let(Name::identifier) }.toList()
+
+    override fun findInnerClass(name: Name) = klass.declaredClasses
+            .asSequence()
+            .firstOrNull {
+                it.simpleName == name.asString()
+            }?.let(::ReflectJavaClass)
 
     override val fqName: FqName
         get() = klass.classId.asSingleFqName()