time: move RFC 3339 optimizations to separate file
The optimizations were added in CL 425197 and CL 421877.
Move this functionality to a separate file to keep format.go smaller
and to document the justification for why this optimization exists.
Change-Id: I1e4e1ace19f9d596d8c0cf49ab6062f63a87b5bf
Reviewed-on: https://go-review.googlesource.com/c/go/+/430675
Run-TryBot: Joseph Tsai <joetsai@digital-static.net>
Auto-Submit: Jenny Rakoczy <jenny@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Rob Pike <r@golang.org> Reviewed-by: Jenny Rakoczy <jenny@golang.org> Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Jenny Rakoczy <jenny@golang.org>
Auto-Submit: Joseph Tsai <joetsai@digital-static.net>