a real core shutdown of a CQ until such requests are done

Change names to StreamedUnary, ServerUnaryStreamer, etc. Use a templated method handler since most code shared between the new StreamedUnary and the existing BidiStreaming. Eliminate the separate enum case for streamed unary. Return a status failure if a StreamedUnary method handler doesn't actually do a write (since that is
violating the appearance of unary-ness)

ServerReaderWriterInterface so that some functions can be made
to accept either.

streaming (sync and async) APIs

Add the option of adding a non-listening server completion queue. This makes writing certain test cases (like hybrid_end2end tests) easier

There is a comment above IsCancelled that says when it is ok to use this.

In some cases, the prototype argument order was different
than the declaration order.

Based on a patch from Sam Leffler.

Original PR #3074 by @dgquintas

Minor fixes to previously existing docs.

Use it to validate that arithmetic on time types makes even some vague
kind of sense.