Utils: Replace FilePath::onDevice() by new FilePath::withMappedPath()

Basically a.onDevice(b) == b.withNewMappedPath(a), matching the order
of b.withNewPath(a).

Whether the (curretly docker-specific) path mapping is useful /there/, and
whether some of the calls are needed at all is dubious. I added some
FIXME and changed a few cases directly.

Change-Id: I7514736ce922f632f1f737bc496f6783389a42b6
Reviewed-by: Marcus Tillmanns <marcus.tillmanns@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>

src/plugins/cmakeprojectmanager/cmakebuildconfiguration.cpp

@@ -701,7 +701,7 @@ void CMakeBuildSettingsWidget::updateConfigureDetailsWidgetsSummary(
     const FilePath buildDirectory = bc ? bc->buildDirectory() : ".";
 
     cmd.addArgs({"-S", m_buildSystem->projectDirectory().path()});
-    cmd.addArgs({"-B", buildDirectory.onDevice(cmd.executable()).path()});
+    cmd.addArgs({"-B", cmd.executable().withNewMappedPath(buildDirectory).path()}); // FIXME: Just buildDirectory.path()
     cmd.addArgs(configurationArguments);
 
     params.setCommandLine(cmd);