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

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



Change-Id: I402826ff56c7f3db71143e9c121db8f427d2ba7c
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>