cmd/go: add Context parameter to base.command.Run

One small step to start propagating the context in
cmd/go for tracing purposes.

Updates #38714

Change-Id: Ibb6debeb9233f84d55f0e81244487355cbe7b82c
Reviewed-on: https://go-review.googlesource.com/c/go/+/237684


Run-TryBot: Michael Matloob <matloob@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>
Reviewed-by: Bryan C. Mills <bcmills@google.com>