text/template: support range-over-int

text/template: support range-over-int

Fixes #66107

Change-Id: I19b466e3fb17557cf4f198b7fd8c13e774d854b1
Reviewed-on: https://go-review.googlesource.com/c/go/+/615095
Auto-Submit: Ian Lance Taylor <iant@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>
Commit-Queue: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>