Source.getDefaultOutputCoder() - hard to implement for adapter style sources #18202
Description
Knowing that you can throw CannotProviderCoderException is an important part of implementing getDefaultOutputCoder
The documentation for PTransform's getDefaultOutputCoder mentions this class, and we should do this for the Source class as well.
Imported from Jira BEAM-1166. Original Jira may contain additional context.
Reported by: sisk.