[XSwiftBus] Add getVersionNumber to DBus API

This allows to get the version number of XSwiftBus itself. It maintains the same version as swift (e.g. 0.8.7 without the time stamp) and can be used to compare it for compatibility reasons.

ref T394

src/xswiftbus/org.swift_project.xswiftbus.service.xml

@@ -1,5 +1,8 @@
 R"(<node>
   <interface name="org.swift_project.xswiftbus.service">
+    <method name="getVersionNumber">
+      <arg type="s" direction="out"/>
+    </method>
     <method name="addTextMessage">
       <arg name="text" type="s" direction="in"/>
       <arg name="red" type="d" direction="in"/>

src/xswiftbus/service.cpp

@@ -207,7 +207,14 @@ namespace XSwiftBus
         }
         else if (message.getInterfaceName() == XSWIFTBUS_SERVICE_INTERFACENAME)
         {
-            if (message.getMethodName() == "addTextMessage")
+            if (message.getMethodName() == "getVersionNumber")
+            {
+                queueDBusCall([ = ]()
+                {
+                    sendDBusReply(sender, serial, getVersionNumber());
+                });
+            }
+            else if (message.getMethodName() == "addTextMessage")
             {
                 maybeSendEmptyDBusReply(wantsReply, sender, serial);
                 std::string text;

src/xswiftbus/service.h

@@ -61,6 +61,9 @@ namespace XSwiftBus
         //! Called by XPluginReceiveMessage when the model changes.
         void onAircraftModelChanged();
 
+        //! Returns the XSwiftBus version number
+        std::string getVersionNumber() const { return XSWIFTBUS_VERSION; }
+
         //! Add a text message to the on-screen display, with RGB components in the range [0,1]
         void addTextMessage(const std::string &text, double red, double green, double blue);
 

src/xswiftbus/xswiftbus.pro

@@ -72,6 +72,8 @@ DEFINES += XPLM210=1
 DEFINES += XPMP_CLIENT_NAME=\\\"xswiftbus\\\"
 DEFINES += XPMP_CLIENT_LONGNAME=\\\"xswiftbus\\\"
 
+DEFINES += XSWIFTBUS_VERSION=\\\"$${BLACK_VERSION}\\\"
+
 # X-Plane plugins must follow a prescribed filename and directory structure.
 TARGET_EXT = .xpl
 win32:TARGET = win