cmd/compile/internal/devirtualize: sort equal weight CallStat.Hottest by name

cmd/compile/internal/devirtualize: sort equal weight CallStat.Hottest by name

When two callees have equal weight, we need to sort by another criteria
to ensure that we get stable output.

Note that this is only for the CallStat debug JSON output. The actual
callee selection already does this secondary sort in
findHotConcreteCallee.

Change-Id: I0de105623c5ccc793ca6f5799ea25e57bc286722
Reviewed-on: https://go-review.googlesource.com/c/go/+/527796
Auto-Submit: Michael Pratt <mpratt@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>