The dataset writer needs an LRU cache to keep track of open files so that it can respect a "max open files" property (see ARROW-12321). A synchronous LruCache implementation already exists but on eviction from the cache we need to wait until all pending writes have completed before we evict the item and open a new file. This ticket is to create an AsyncLruCache which will allow the creation of items and the eviction of items to be asynchronous.

Reporter: Weston Pace / @westonpace
Assignee: Weston Pace / @westonpace

_{Note: This issue was originally created as ARROW-13644. Please see the migration documentation for further details.}