cmd/internal/script/scriptest: add new apis for tool test use
Add top level apis to provide a general-purpose "script test" runner
for clients within cmd, e.g. tools such as compile, link, nm, and so
on. This patch doesn't add any uses of the new apis, this will
happen in follow-on CLs.
Updates #68606.
Change-Id: Ib7200a75d4dc7dc50897628f1a6269937be15a76
Reviewed-on: https://go-review.googlesource.com/c/go/+/601359 Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Cherry Mui <cherryyz@google.com>