internal/sync: add Range to HashTrieMap

internal/sync: add Range to HashTrieMap

This implementation is trivial given that All already exists. The
purpose of Range is to conform to sync.Map's API.

Change-Id: Icfe755b9986c46b88c7201644e562b1631a02b66
Reviewed-on: https://go-review.googlesource.com/c/go/+/606460
Reviewed-by: David Chase <drchase@google.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>