Utils: Add CommandLine convenience constructors

... taking a QString for the executable.

This weakens the very explicit QString -> FileName conversion via the
named constructors for the special case of constructing a CommandLine.

I think that's worthwhile here, as it reduces the noise on the caller
site under circumstance where the nature of the thing is obvious.

Change-Id: I27b4a73639728893d053b2e7ba65cb745f0ffe83
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/debugger/debuggeritemmanager.cpp

@@ -759,8 +759,7 @@ void DebuggerItemManagerPrivate::autoDetectGdbOrLldbDebuggers()
     if (HostOsInfo::isMacHost()) {
         SynchronousProcess lldbInfo;
         lldbInfo.setTimeoutS(2);
-        SynchronousProcessResponse response
-            = lldbInfo.runBlocking(CommandLine(FilePath::fromString("xcrun"), {"--find", "lldb"}));
+        SynchronousProcessResponse response = lldbInfo.runBlocking({"xcrun", {"--find", "lldb"}});
         if (response.result == Utils::SynchronousProcessResponse::Finished) {
             QString lPath = response.allOutput().trimmed();
             if (!lPath.isEmpty()) {