Changes to exec_ctx/closure/combiner/workqueue interfaces

attach trailing metadata to ruby bidi call op when it's received

change ruby default unimplemented ruby server handler to have two aguments

remove test of exception on ruby thread pool overload

Revert "Revert "Reduce memory bloat (each server cq is very expensive)""

No need for copyright on generated files

PHP: fix code style

Update Python examples with fresh generated code.

Rename interop-as-a-unit-test "intraop".

Set Python documentation copyright

It's been confusing that these tests have been called "interop" but
are not actually tests of interoperation.

Merge pull request #9206 from soltanmm-google/is-the-world-is-moving-too-fast-or-am-I-moving-too-slow

Add `auto-gen`d comment to `_pb2_grpc.py` files

Remove for loop initial declarations

Some of these files contain the magic string "DO NOT EDIT" but we do
not wish for our tests to depend upon that.

- make closures know where they should be executed (eg, on a workqueue,
  or a combiner, or on an exec_ctx)
- this allows removal of a large number of trampoline functions that
  were appearing whenever we used combiners, and should allow for a much
  easier interface to combiner locks

Check and fail if user provides a metadata key starting with :

Fix jwt verifier