Improve logging while calling core API (#32059)

* Improve logging while calling core API

* Use NULL for _core_error_string

* Don't raise inside Exception hanlder

* Changes based on comment

* Remove unused enum

* Decode and add qoutes for grpc_call_error_string.

src/python/grpcio/grpc/_cython/_cygrpc/aio/callback_common.pyx.pxi

@@ -93,7 +93,8 @@ async def execute_batch(GrpcCallWrapper grpc_call_wrapper,
         wrapper.c_functor(), NULL)
 
     if error != GRPC_CALL_OK:
-        raise ExecuteBatchError("Failed grpc_call_start_batch: {}".format(error))
+        grpc_call_error_string = grpc_call_error_to_string(error).decode()
+        raise ExecuteBatchError("Failed grpc_call_start_batch: {} with grpc_call_error value: '{}'".format(error, grpc_call_error_string))
 
     await future
 

src/python/grpcio/grpc/_cython/_cygrpc/aio/server.pyx.pxi

@@ -716,14 +716,18 @@ async def _handle_exceptions(RPCState rpc_state, object rpc_coro, object loop):
                 status_code = rpc_state.status_code
 
             rpc_state.status_sent = True
-            await _send_error_status_from_server(
-                rpc_state,
-                status_code,
-                'Unexpected %s: %s' % (type(e), e),
-                rpc_state.trailing_metadata,
-                rpc_state.create_send_initial_metadata_op_if_not_sent(),
-                loop
-            )
+            try:
+                await _send_error_status_from_server(
+                    rpc_state,
+                    status_code,
+                    'Unexpected %s: %s' % (type(e), e),
+                    rpc_state.trailing_metadata,
+                    rpc_state.create_send_initial_metadata_op_if_not_sent(),
+                    loop
+                )
+            except ExecuteBatchError:
+                _LOGGER.exception('Failed sending error status from server')
+                traceback.print_exc()
 
 
 cdef _add_callback_handler(object rpc_task, RPCState rpc_state):

src/python/grpcio/grpc/_cython/_cygrpc/grpc.pxi

@@ -396,6 +396,7 @@ cdef extern from "grpc/grpc.h":
   grpc_call_error grpc_call_start_batch(
       grpc_call *call, const grpc_op *ops, size_t nops, void *tag,
       void *reserved) nogil
+  const char* grpc_call_error_to_string(grpc_call_error error) nogil
   grpc_call_error grpc_call_cancel(grpc_call *call, void *reserved) nogil
   grpc_call_error grpc_call_cancel_with_status(grpc_call *call,
                                                grpc_status_code status,