html/template, text/template: implement break and continue for range loops
Break and continue for range loops was accepted as a proposal in June 2017.
It was implemented in CL 66410 (Oct 2017)
but then rolled back in CL 92155 (Feb 2018)
because html/template changes had not been implemented.
This CL reimplements break and continue in text/template
and then adds support for them in html/template as well.
Fixes #20531.
Change-Id: I05330482a976f1c078b4b49c2287bd9031bb7616
Reviewed-on: https://go-review.googlesource.com/c/go/+/321491
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Rob Pike <r@golang.org>