Prepare for the new batch call API.

Rename all core API functions that are on their way to deprecation with
an _old tag across all wrappings.
diff --git a/test/core/end2end/tests/max_concurrent_streams.c b/test/core/end2end/tests/max_concurrent_streams.c
index a177a7b..0e26577 100644
--- a/test/core/end2end/tests/max_concurrent_streams.c
+++ b/test/core/end2end/tests/max_concurrent_streams.c
@@ -109,27 +109,29 @@
   cq_verifier *v_client = cq_verifier_create(f.client_cq);
   cq_verifier *v_server = cq_verifier_create(f.server_cq);
 
-  c = grpc_channel_create_call(f.client, "/foo", "test.google.com", deadline);
+  c = grpc_channel_create_call_old(f.client, "/foo", "test.google.com",
+                                   deadline);
   GPR_ASSERT(c);
 
   GPR_ASSERT(GRPC_CALL_OK ==
-             grpc_call_invoke(c, f.client_cq, tag(2), tag(3), 0));
+             grpc_call_invoke_old(c, f.client_cq, tag(2), tag(3), 0));
 
-  GPR_ASSERT(GRPC_CALL_OK == grpc_call_writes_done(c, tag(4)));
+  GPR_ASSERT(GRPC_CALL_OK == grpc_call_writes_done_old(c, tag(4)));
   cq_expect_finish_accepted(v_client, tag(4), GRPC_OP_OK);
   cq_verify(v_client);
 
-  GPR_ASSERT(GRPC_CALL_OK == grpc_server_request_call(f.server, tag(100)));
+  GPR_ASSERT(GRPC_CALL_OK == grpc_server_request_call_old(f.server, tag(100)));
   cq_expect_server_rpc_new(v_server, &s, tag(100), "/foo", "test.google.com",
                            deadline, NULL);
   cq_verify(v_server);
 
-  GPR_ASSERT(GRPC_CALL_OK == grpc_call_server_accept(s, f.server_cq, tag(102)));
-  GPR_ASSERT(GRPC_CALL_OK == grpc_call_server_end_initial_metadata(s, 0));
+  GPR_ASSERT(GRPC_CALL_OK ==
+             grpc_call_server_accept_old(s, f.server_cq, tag(102)));
+  GPR_ASSERT(GRPC_CALL_OK == grpc_call_server_end_initial_metadata_old(s, 0));
   cq_expect_client_metadata_read(v_client, tag(2), NULL);
   cq_verify(v_client);
 
-  GPR_ASSERT(GRPC_CALL_OK == grpc_call_start_write_status(
+  GPR_ASSERT(GRPC_CALL_OK == grpc_call_start_write_status_old(
                                  s, GRPC_STATUS_UNIMPLEMENTED, "xyz", tag(5)));
   cq_expect_finished_with_status(v_client, tag(3), GRPC_STATUS_UNIMPLEMENTED,
                                  "xyz", NULL);
@@ -181,20 +183,21 @@
   /* start two requests - ensuring that the second is not accepted until
      the first completes */
   deadline = five_seconds_time();
-  c1 =
-      grpc_channel_create_call(f.client, "/alpha", "test.google.com", deadline);
+  c1 = grpc_channel_create_call_old(f.client, "/alpha", "test.google.com",
+                                    deadline);
   GPR_ASSERT(c1);
-  c2 = grpc_channel_create_call(f.client, "/beta", "test.google.com", deadline);
+  c2 = grpc_channel_create_call_old(f.client, "/beta", "test.google.com",
+                                    deadline);
   GPR_ASSERT(c1);
 
-  GPR_ASSERT(GRPC_CALL_OK == grpc_server_request_call(f.server, tag(100)));
+  GPR_ASSERT(GRPC_CALL_OK == grpc_server_request_call_old(f.server, tag(100)));
 
   GPR_ASSERT(GRPC_CALL_OK ==
-             grpc_call_invoke(c1, f.client_cq, tag(301), tag(302), 0));
+             grpc_call_invoke_old(c1, f.client_cq, tag(301), tag(302), 0));
   GPR_ASSERT(GRPC_CALL_OK ==
-             grpc_call_invoke(c2, f.client_cq, tag(401), tag(402), 0));
-  GPR_ASSERT(GRPC_CALL_OK == grpc_call_writes_done(c1, tag(303)));
-  GPR_ASSERT(GRPC_CALL_OK == grpc_call_writes_done(c2, tag(303)));
+             grpc_call_invoke_old(c2, f.client_cq, tag(401), tag(402), 0));
+  GPR_ASSERT(GRPC_CALL_OK == grpc_call_writes_done_old(c1, tag(303)));
+  GPR_ASSERT(GRPC_CALL_OK == grpc_call_writes_done_old(c2, tag(303)));
 
   ev = grpc_completion_queue_next(
       f.client_cq, gpr_time_add(gpr_now(), gpr_time_from_seconds(10)));
@@ -213,14 +216,14 @@
   cq_verify(v_server);
 
   GPR_ASSERT(GRPC_CALL_OK ==
-             grpc_call_server_accept(s1, f.server_cq, tag(102)));
-  GPR_ASSERT(GRPC_CALL_OK == grpc_call_server_end_initial_metadata(s1, 0));
+             grpc_call_server_accept_old(s1, f.server_cq, tag(102)));
+  GPR_ASSERT(GRPC_CALL_OK == grpc_call_server_end_initial_metadata_old(s1, 0));
   cq_expect_client_metadata_read(v_client, tag(live_call + 1), NULL);
   cq_verify(v_client);
 
   GPR_ASSERT(GRPC_CALL_OK ==
-             grpc_call_start_write_status(s1, GRPC_STATUS_UNIMPLEMENTED, "xyz",
-                                          tag(103)));
+             grpc_call_start_write_status_old(s1, GRPC_STATUS_UNIMPLEMENTED,
+                                              "xyz", tag(103)));
   cq_expect_finish_accepted(v_server, tag(103), GRPC_OP_OK);
   cq_expect_finished(v_server, tag(102), NULL);
   cq_verify(v_server);
@@ -232,21 +235,21 @@
   live_call = (live_call == 300) ? 400 : 300;
   cq_verify(v_client);
 
-  GPR_ASSERT(GRPC_CALL_OK == grpc_server_request_call(f.server, tag(200)));
+  GPR_ASSERT(GRPC_CALL_OK == grpc_server_request_call_old(f.server, tag(200)));
   cq_expect_server_rpc_new(v_server, &s2, tag(200),
                            live_call == 300 ? "/alpha" : "/beta",
                            "test.google.com", deadline, NULL);
   cq_verify(v_server);
 
   GPR_ASSERT(GRPC_CALL_OK ==
-             grpc_call_server_accept(s2, f.server_cq, tag(202)));
-  GPR_ASSERT(GRPC_CALL_OK == grpc_call_server_end_initial_metadata(s2, 0));
+             grpc_call_server_accept_old(s2, f.server_cq, tag(202)));
+  GPR_ASSERT(GRPC_CALL_OK == grpc_call_server_end_initial_metadata_old(s2, 0));
   cq_expect_client_metadata_read(v_client, tag(live_call + 1), NULL);
   cq_verify(v_client);
 
   GPR_ASSERT(GRPC_CALL_OK ==
-             grpc_call_start_write_status(s2, GRPC_STATUS_UNIMPLEMENTED, "xyz",
-                                          tag(203)));
+             grpc_call_start_write_status_old(s2, GRPC_STATUS_UNIMPLEMENTED,
+                                              "xyz", tag(203)));
   cq_expect_finish_accepted(v_server, tag(203), GRPC_OP_OK);
   cq_expect_finished(v_server, tag(202), NULL);
   cq_verify(v_server);