[GWP-ASan] Move random-related code in the allocator (redo) am: 1a535e259f am: 68c3dbcc7b

Original change: https://android-review.googlesource.com/c/platform/external/gwp_asan/+/1506200

Change-Id: Idef82e6f4a2447529cb96ab150470a9317370e56