[gbinder] Add "aidl4" variant of service manager

Introduce "aidl4" variant of service manager to adapt the change
to service related protocol for Android 12.

From Android 12, when reading nullable strong binder, the format of
the `stability` field passed on the wire was changed and evolved to
`struct Category`, which consists of the following members with 4 bytes long.
```
struct Category {
  uint8_t version;
  uint8_t reserved[2];
  Level level;        <- bitmask of Stability::Level
}
```
Please check the following link for details:

  https://cs.android.com/android/platform/superproject/+/android-12.0.0_r3:frameworks/native/libs/binder/include/binder/Stability.h;l=140

To honor the change on AOSP side for Android 12, we need to adapt
the protocol change in Service Manager.

Makefile

@@ -105,6 +105,7 @@ SRC += \
   gbinder_servicemanager_aidl.c \
   gbinder_servicemanager_aidl2.c \
   gbinder_servicemanager_aidl3.c \
+  gbinder_servicemanager_aidl4.c \
   gbinder_servicemanager_hidl.c
 
 SRC += \