Make documentation bzl_library publicly visible

[shs96c]

This allows anyone who depends on rules_jvm_external and imports
"something" from these rules into their own rules to be able to
generate stardoc of their own functions.

I've filed bazelbuild/stardoc#93 to track
this issue. Once it's fixed, we can close this.

[jin]

I'm not comfortable for exposing this target because it's meant for RJE-internal docs. If you really need a file, could you create a temporary target with the minimum set of files you need, and expose that instead?

[shs96c]

The way that stardoc works it that anything that transitively depends upon rules_jvm_external needs to include our bzl files in a bzl_library. Either we need to expose all those files publicly using something like exports_files or we make this rule visible. Exporting the files ties those rules even more intimately to the internals of this ruleset, which is undesirable.

Without this change, any rule that depends upon rules_jvm_external (such as Selenium's own rules) cannot be documented using stardoc. That's why I filed bazelbuild/stardoc#93 and that's why I'm making this change.

[shs96c]

Also, to create the temporary target, one would need to patch rules_jvm_external since there are build files in our tree, preventing us from just "reaching in and taking what we need"

[jin]

Looks like there's a plan to support bazelbuild/stardoc#93, but work needs to be done to get there. For this PR, could you at least document that the bzl_library is public for stardoc and stardoc only?