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/perfprofiler/perftracepointdialog.cpp

@@ -41,11 +41,12 @@
 #include <QPushButton>
 #include <QTimer>
 
+using namespace ProjectExplorer;
+using namespace Utils;
+
 namespace PerfProfiler {
 namespace Internal {
 
-using namespace ProjectExplorer;
-
 PerfTracePointDialog::PerfTracePointDialog() :
     m_ui(new Ui::PerfTracePointDialog)
 {
@@ -102,7 +103,7 @@ void PerfTracePointDialog::runScript()
     Runnable runnable;
     const QString elevate = m_ui->privilegesChooser->currentText();
     if (elevate != QLatin1String("n.a."))
-        runnable.command = {elevate, {"sh"}};
+        runnable.command = {FilePath::fromString(elevate), {"sh"}};
     else
         runnable.command = {"sh", {}};