Abstract Coder translation from Runner API Protos

Instead of having a large switch statement that constructs known coders, have a map from URN to an interface that takes `(RunnerApi.Coder, RunnerApi.Components)` and produces a java Coder, and delegate all calls in `fromProto` to that map.

Imported from Jira [BEAM-1930](https://issues.apache.org/jira/browse/BEAM-1930). Original Jira may contain additional context.
Reported by: tgroh.

Start by locating fromProto and its current switch over coder URNs, then inspect the RunnerApi.Coder and RunnerApi.Components types it receives. Done means supported URNs are delegated through the proposed map while preserving the existing coder translation behavior.

Written by the indexing model from the issue text.