Allow a placeholder in programmatic go links to include slashes

[nsinghfigma]

Right now in a programmatic go link, a %s will only include text in between slashes.

For example:
If go/cs/%s -> https://cs.github.com/?q=%s
then go/cs/blah will redirect me to https://cs.github.com/?q=blah
but go/cs/foo/bar will not redirect to https://cs.github.com/?q=foo/bar. (This is particularly relevant when searching for file paths.)

We'd probably need another placeholder token (maybe%q?) as to not conflict with allowing multiple placeholders.

For now one verbose workaround is to do something like:
go/cs/%s -> https://cs.github.com/?q=%s
go/cs/%s/%s -> https://cs.github.com/?q=%s/%s
go/cs/%s/%s/%s -> https://cs.github.com/?q=%s/%s/%s
go/cs/%s/%s/%s/%s -> https://cs.github.com/?q=%s/%s/%s/%s
... until you get to the max depth that you care about.