Utils: Introduce a FilePath constructor from char arrays

Similar to QT_RESTRICTED_CAST_FROM_ASCII to avoid the need for
decorations in user code.

At the same time, drop some convenience constructors and functions
in CommandLine and Icon essentially serving the same purpose.

Change-Id: Ida4e5ac19c2da0a4298a97b2a8e1511d56bbb79d
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/docker/dockerdevice.cpp

@@ -214,7 +214,7 @@ class DockerPortsGatheringMethod : public PortsGatheringMethod
 
         // /proc/net/tcp* covers /proc/net/tcp and /proc/net/tcp6
         Runnable runnable;
-        runnable.command.setExecutable(FilePath::fromString("sed"));
+        runnable.command.setExecutable("sed");
         runnable.command.setArguments("-e 's/.*: [[:xdigit:]]*:\\([[:xdigit:]]\\{4\\}\\).*/\\1/g' /proc/net/tcp*");
         return runnable;
     }