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

compiler/frontend.java/src/org/jetbrains/kotlin/load/java/structure/impl/JavaClassImpl.kt

@@ -31,8 +31,12 @@ class JavaClassImpl(psiClass: PsiClass) : JavaClassifierImpl<PsiClass>(psiClass)
         assert(psiClass !is PsiTypeParameter) { "PsiTypeParameter should be wrapped in JavaTypeParameter, not JavaClass: use JavaClassifier.create()" }
     }
 
-    override val innerClasses: Collection<JavaClass>
-        get() = classes(psi.innerClasses)
+    override val innerClassNames: Collection<Name>
+        get() = psi.innerClasses.mapNotNull { it.name?.takeIf(Name::isValidIdentifier)?.let(Name::identifier) }
+
+    override fun findInnerClass(name: Name): JavaClass? {
+        return psi.findInnerClassByName(name.asString(), false)?.let(::JavaClassImpl)
+    }
 
     override val fqName: FqName?
         get() {