Let users use `Striped` with a custom `Supplier` (Make `Striped.custom` `public`?)

[burstinair]

hi, i thinkcom.google.common.util.concurrent.Striped is a great tool, but why i couldn't use its lazy method to custom the supplier?
i just want to use Striped with my custom lock, but i found it's impossible, so should we make lazy a public access method?

[cpovirk]

We also considered Striped<RateLimiter> to replace the internal ThrottleSet class, and we might want Striped<Monitor>. Generic support is probably worth adding, but it probably won't be a priority for us in the near future. We could take a patch from someone who's signed the CLA.

[thecoop]

Striped<L> is a generally useful class that could be used for a fair number of things, including custom lock implementations. It would be good if this was accessible.