[refactor] Apply forward declaration as much as possible (#64)

* [refactor] Apply forward declaration as much as possible

Fixes #60

### Motivation

The includes in pulsar-client-cpp is very casual. There are a lot of
implicit includes and the forward declaration is not used much. For
example, if `lib/ClientConnection.h` was modified, 27 files would be
recompiled.

The other problem is the `SortIncludes` attribute in `.clang-format`
file is false. It might be okay in early days. However, as the project
grows, including many headers without ordering brings a very bad
experience. Combining with the very few usages of the forward
declaration, it's hard to determine whether a header is still required
after a change.

### Modifications

Apply forward declarations as much as possible and change the
`SortIncludes` to true in `.clang-format` file.

It's special for the `PulsarApi.pb.h` file because the size of this
header is over 1 MiB. For classes we can use forward declaration, but
for enumerations we have to include this header.

To solve this problem, `ProtoApiEnums.h` is added to define some
constant integers that can be cast implicitly from the enumerations. If
we want to use enumerations from `PulsarApi.pb.h`, we can include
`ProtoApiEnums.h` instead.

Finally, to unify the include rules, in `lib/*.h`, if we want to include
a header (e.g. `xxx.h`) from the same directory, just use `#include
"xxx.h"`. Don't use `#include "lib/xxx.h"` or `#include <lib/xxx.h>` in
headers of `lib/` directory.

### Improvements

Since forward declaration is applied everywhere now, take
`lib/ClientConnection.h` for example. After this patch, only 10 files
needs to be recompiled, while 27 files would be recompiled before.

This patch also reduces the binary size and speeds up the compilation
time.

Binary size:
- `libpulsar.a`: 319234696 (305 MiB) -> 286716564 (274 MiB)
- `libpulsar.so`: 110162496 (106 MiB) -> 102428456 (98 MiB)

Compilation time with the following commands:

```bash
cmake -B build -DBUILD_TESTS=OFF
cmake --build build -j8
```

* Fix MSVC build

Author: BewareMyPower

.clang-format

@@ -19,7 +19,7 @@
 BasedOnStyle: Google
 IndentWidth: 4
 ColumnLimit: 110
-SortIncludes: false
+SortIncludes: true
 BreakBeforeBraces: Custom
 BraceWrapping:
   AfterEnum: true

examples/SampleAsyncProducer.cc

@@ -16,12 +16,12 @@
  * specific language governing permissions and limitations
  * under the License.
  */
+#include <pulsar/Client.h>
+
 #include <iostream>
 #include <thread>
 
-#include <pulsar/Client.h>
-
-#include <lib/LogUtils.h>
+#include "lib/LogUtils.h"
 
 DECLARE_LOG_OBJECT()
 

examples/SampleConsumer.cc

@@ -16,11 +16,11 @@
  * specific language governing permissions and limitations
  * under the License.
  */
-#include <iostream>
-
 #include <pulsar/Client.h>
 
-#include <lib/LogUtils.h>
+#include <iostream>
+
+#include "lib/LogUtils.h"
 
 DECLARE_LOG_OBJECT()
 

examples/SampleConsumerListener.cc

@@ -16,11 +16,11 @@
  * specific language governing permissions and limitations
  * under the License.
  */
-#include <iostream>
-
 #include <pulsar/Client.h>
 
-#include <lib/LogUtils.h>
+#include <iostream>
+
+#include "lib/LogUtils.h"
 
 DECLARE_LOG_OBJECT()
 

examples/SampleProducer.cc

@@ -16,11 +16,11 @@
  * specific language governing permissions and limitations
  * under the License.
  */
-#include <iostream>
-
 #include <pulsar/Client.h>
 
-#include <lib/LogUtils.h>
+#include <iostream>
+
+#include "lib/LogUtils.h"
 
 DECLARE_LOG_OBJECT()
 

include/pulsar/Authentication.h

@@ -19,13 +19,14 @@
 #ifndef PULSAR_AUTHENTICATION_H_
 #define PULSAR_AUTHENTICATION_H_
 
+#include <pulsar/Result.h>
 #include <pulsar/defines.h>
-#include <vector>
-#include <string>
+
+#include <functional>
 #include <map>
 #include <memory>
-#include <pulsar/Result.h>
-#include <functional>
+#include <string>
+#include <vector>
 
 namespace pulsar {
 

include/pulsar/BatchReceivePolicy.h

@@ -20,6 +20,7 @@
 #define BATCH_RECEIVE_POLICY_HPP_
 
 #include <pulsar/defines.h>
+
 #include <memory>
 
 namespace pulsar {

include/pulsar/BrokerConsumerStats.h

@@ -19,13 +19,13 @@
 #ifndef PULSAR_CPP_BROKERCONSUMERSTATS_H
 #define PULSAR_CPP_BROKERCONSUMERSTATS_H
 
-#include <pulsar/defines.h>
-#include <string.h>
-#include <iostream>
+#include <pulsar/ConsumerType.h>
 #include <pulsar/Result.h>
+#include <pulsar/defines.h>
+
 #include <functional>
+#include <iostream>
 #include <memory>
-#include <pulsar/ConsumerType.h>
 
 namespace pulsar {
 class BrokerConsumerStatsImplBase;

include/pulsar/Client.h

@@ -19,17 +19,18 @@
 #ifndef PULSAR_CLIENT_HPP_
 #define PULSAR_CLIENT_HPP_
 
-#include <pulsar/defines.h>
+#include <pulsar/ClientConfiguration.h>
+#include <pulsar/ConsoleLoggerFactory.h>
 #include <pulsar/Consumer.h>
+#include <pulsar/FileLoggerFactory.h>
+#include <pulsar/Message.h>
+#include <pulsar/MessageBuilder.h>
 #include <pulsar/Producer.h>
 #include <pulsar/Reader.h>
 #include <pulsar/Result.h>
-#include <pulsar/Message.h>
-#include <pulsar/MessageBuilder.h>
-#include <pulsar/ClientConfiguration.h>
 #include <pulsar/Schema.h>
-#include <pulsar/ConsoleLoggerFactory.h>
-#include <pulsar/FileLoggerFactory.h>
+#include <pulsar/defines.h>
+
 #include <string>
 
 namespace pulsar {

include/pulsar/ClientConfiguration.h

@@ -19,9 +19,9 @@
 #ifndef PULSAR_CLIENTCONFIGURATION_H_
 #define PULSAR_CLIENTCONFIGURATION_H_
 
-#include <pulsar/defines.h>
 #include <pulsar/Authentication.h>
 #include <pulsar/Logger.h>
+#include <pulsar/defines.h>
 
 namespace pulsar {
 class PulsarWrapper;