Ruby: improve server error handling, fix a reference error

Improve docs on GRPC_OP_RECV_CLOSE_ON_SERVER

add a dummy service with no rpc to test codegen coverage

Add proto comments to generated _pb2.py files

Removed leftover function declaration from channel args

Fixed name of test config for h2_census

Fix coverage for large message and secure async end2end

Don't try to read files that have been moved/renamed.

Moved protos out of core_codegen interface

As opposed to a flat directory, we now have the following structure:

- security
  -context
  - credentials
    - composite
    - fake
    - google_default
    - iam
    - jwt
    - oauth2
    - plugin
    - ssl
  - transport
  - util

We have not refactored the test code yet but this PR is already large
enough...

C# finishing serverside request stream should not be required to dispose.

Add C# wrapping tests and fix some issues with the API.

Cleanup tools/jenkins directory

Allow directly specifiying connection path