framework.jar file was combined with android.jar from /<SDK location>/platforms/android-X, where X is current API level.

I'm not sure that it will work as intended. If it does not work, please report to us.

========== framework.jar source =========
Device: Oneplus 3T
ROM: LineageOS 16
Date of ROM: Mon Sep 10 2018
Uploader: MrWhite214

================= BACKUP ================

Original android.jar can be downloaded here
http://dl.google.com/android/repository/platform-28_r06.zip

Extract the archive and find android.jar