Simplify reading sets, maps, and lists

[nik9000]

While working on removing ImmutableMap and ImmutableSet I've seen a ton of different fun ways to read immutable maps, sets, and lists. If we're willing to use Java 8's function pointer things we could remove lots of duplicated code by creating readMap, readSet, and readList in StreamInput. We could probably also do something similar for writing these but I haven't thought as much about it.

[jpountz]

+1

[elasticmachine]

Pinging @elastic/es-core-infra

[tomcallahan]

Those methods exist, and we're unlikely to tie an issue to going on a large deduplication effort. Closing.