Abstract prebuilt_etc into prebuilt_file am: b81f77ed am: c0fa5fb3 am:...

Abstract prebuilt_etc into prebuilt_file am: b81f77ed am: c0fa5fb3 am: 30136e83 am: 90bdb0b4

Original change: https://android-review.googlesource.com/c/platform/build/soong/+/2002752



Change-Id: I9c6ef032a9dc7b928c23931f8bf243f7a5d3b7d7
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>