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

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

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



Change-Id: I8b27489fae512e76743eb20dfb92f6334a67d3dc
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>