Init on First Use and Retain LZ4 Contexts
Init on First Use and Retain LZ4 Contexts

Summary:
Reusing a context can provide significant efficiency benefits.

Depends on D8172801.

Reviewed By: yfeldblum, terrelln

Differential Revision: D8172871

fbshipit-source-id: f92c85410a35643502d28922583ee0ed0b4386c9

facebook/folly,facebook/folly,facebook/folly,facebook/folly,facebook/folly