go.mod: upgrade to go 1.17
go.mod: upgrade to go 1.17

This change was produced using 'go mod tidy -go=1.17'
with a go command built at CL 315210.

This activates lazy loading, and updates the go.mod file to maintain
the lazy-loading invariants (namely, including an explicit requirement
for every package transitively imported by the main module).

Note that this does *not* prevent users with earlier go versions from
successfully building packages from this module.

For golang/go#36460

Change-Id: If672eca0dad61b3f6050a94c758d605b6586cbc3
Reviewed-on: https://go-review.googlesource.com/c/mod/+/316113
Trust: Bryan C. Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>
Run-TryBot: Bryan C. Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Michael Matloob <4562438b12c14e81a47550acde616ff328a909f8@golang.org>

golang/mod,golang/mod