Special thanks to INADA Naoki for pushing the patch through
the last mile, Serhiy Storchaka for reviewing the code, and to
Victor Stinner for suggesting the idea (originally implemented
in the PyPy project).

a var-positional argument.  Added opcode BUILD_TUPLE_UNPACK_WITH_CALL.

Issue #27213: Rework CALL_FUNCTION* opcodes to produce shorter and more
efficient bytecode:

* CALL_FUNCTION now only accepts position arguments
* CALL_FUNCTION_KW accepts position arguments and keyword arguments, but keys
  of keyword arguments are packed into a constant tuple.
* CALL_FUNCTION_EX is the most generic, it expects a tuple and a dict for
  positional and keyword arguments.

CALL_FUNCTION_VAR and CALL_FUNCTION_VAR_KW opcodes have been removed.

2 tests of test_traceback are currently broken: skip test, the issue #28050 was
created to track the issue.

Patch by Demur Rumed, design by Serhiy Storchaka, reviewed by Serhiy Storchaka
and Victor Stinner.

Patch by Ivan Levkivskyi.

Patch by Demur Rumed.

Summary of changes:

1. Coroutines now have a distinct, separate from generators
   type at the C level: PyGen_Type, and a new typedef PyCoroObject.
   PyCoroObject shares the initial segment of struct layout with
   PyGenObject, making it possible to reuse existing generators
   machinery.  The new type is exposed as 'types.CoroutineType'.

   As a consequence of having a new type, CO_GENERATOR flag is
   no longer applied to coroutines.

2. Having a separate type for coroutines made it possible to add
   an __await__ method to the type.  Although it is not used by the
   interpreter (see details on that below), it makes coroutines
   naturally (without using __instancecheck__) conform to
   collections.abc.Coroutine and collections.abc.Awaitable ABCs.

   [The __instancecheck__ is still used for generator-based
   coroutines, as we don't want to add __await__ for generators.]

3. Add new opcode: GET_YIELD_FROM_ITER.  The opcode is needed to
   allow passing native coroutines to the YIELD_FROM opcode.

   Before this change, 'yield from o' expression was compiled to:

      (o)
      GET_ITER
      LOAD_CONST
      YIELD_FROM

   Now, we use GET_YIELD_FROM_ITER instead of GET_ITER.

   The reason for adding a new opcode is that GET_ITER is used
   in some contexts (such as 'for .. in' loops) where passing
   a coroutine object is invalid.

4. Add two new introspection functions to the inspec module:
   getcoroutinestate(c) and getcoroutinelocals(c).

5. inspect.iscoroutine(o) is updated to test if 'o' is a native
   coroutine object.  Before this commit it used abc.Coroutine,
   and it was requested to update inspect.isgenerator(o) to use
   abc.Generator; it was decided, however, that inspect functions
   should really be tailored for checking for native types.

6. sys.set_coroutine_wrapper(w) API is updated to work with only
   native coroutines.  Since types.coroutine decorator supports
   any type of callables now, it would be confusing that it does
   not work for all types of coroutines.

7. Exceptions logic in generators C implementation was updated
   to raise clearer messages for coroutines:

   Before: TypeError("generator raised StopIteration")
   After: TypeError("coroutine raised StopIteration")