make go_reset_target public

[tyler-french]

go_reset_target is helpful when certain plugins or tool attributes to rules can't build under certain configurations. For example, many thrift plugins fail to build when a dependency of a go_binary with c-shared instrumentation.

To alleviate this issue, you can pass the tool to go_reset_target.

[fmeum]

I generally support this, we should thus make sure that the docs comment makes sense for external users.