internal/coverage: use 128-bit FNV-1a hash instead of MD5
This change replaces the MD5 hash used to identify coverage files with a
128-bit FNV-1a hash. This change is motivated by the fact that MD5
should only be used for legacy cryptographic purposes.
The 128-bit FNV-1a hash is sufficient for the purpose of identifying
coverage files, it having the same theoretical collision resistance as
MD5, but with the added benefit of being faster to compute.
Change-Id: I7b547ce2ea784f8f4071599a10fcb512b87ee469
Reviewed-on: https://go-review.googlesource.com/c/go/+/617360
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Than McIntosh <thanm@golang.org> Reviewed-by: Ian Lance Taylor <iant@google.com> Reviewed-by: Cherry Mui <cherryyz@google.com>