Merge "list all valid flags (commands) to soong_ui upon unknown command" am:...

Merge "list all valid flags (commands) to soong_ui upon unknown command" am: b3af19ca am: 996117ca am: cca93ea0 am: 55b48764

Original change: https://android-review.googlesource.com/c/platform/build/soong/+/1965381

Change-Id: Ie5a4ba244e85140156dffdbe00b16b8d33cc8588