I only wanted this in one place, but thought we might as well do it
all in one go.
In a couple of places I added an explicit edition instead of using the
default (whatever that is).
See https://doc.rust-lang.org/edition-guide/rust-2021/index.html.
Test: find . -name "Android.bp" -type f|xargs grep edition | grep -v 2021
Test: atest ComposHostTestCases MicrodroidHostTestCases
Change-Id: I4de050078b303cc5614d230e0d36d5454d60a807
6472ccd6e5