Utils: Extract a CommandLine structure from a QtcProcess

We regularly pass around strings or filenames or pairs of strings
or filenames and stringlist etc the in the end will be used
as a kind of "command line", with quite a bit of ad-hoc user
code and QtcProcess::addArg etc to set them up and manipulate them.

Let's have a class for that concept.

Change-Id: I288ab939d853b32c717135a65242c584c2beab50
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/debugger/debuggerruncontrol.cpp

@@ -113,7 +113,7 @@ public:
 
     void start() override
     {
-        m_proc.setCommand(m_runnable.executable, m_runnable.commandLineArguments);
+        m_proc.setCommand(m_runnable.commandLine());
         m_proc.start();
     }