add batchingGlobal, post-2.13.4

[SethTisue]

now that https://github.com/scala/scala/pull/9270 has landed, and after 2.13.4 ships, we'll want to add batchingGlobal from https://github.com/scala/scala/pull/9132/commits/9e4f6b2173bc9a17cf79bb7a1439b8b62d316a8b here

in the meantime, we'll recommend people just paste the code into their codebases

cc @lrytz

[NthPortal]

labeling this as bug since it's kind of something that's broken/missing as of 2.13.4

also, it looks like we're clear to add it at this point