Merge "Move variable assignment handling to generation context" am: 7cd255fa...

Merge "Move variable assignment handling to generation context" am: 7cd255fa am: 34ce0f3b am: fd387a97 am: 7587df14

Original change: https://android-review.googlesource.com/c/platform/build/soong/+/2057162



Change-Id: Ib707a98db61af41374b23f24c8d659b861a648dc
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>