Use R.txt files from aar files directly

Use the R.txt files from aar imports directly instead of recreating
one using aapt2 from the embedded resources.  Fixes an issue with
com.google.android.material where the jar was referencing
com.google.android.material.R.attr.theme, aapt2 was not producing
"int attr theme 0x0" in R.txt, but the aar's R.txt had it.

Bug: 294256649
Test: builds
Change-Id: Ibe1e5535a75eed59f3b8dbbc12eff9c07af51d37