sysprof: start on SysprofTimeScrubber

This is going to be used to bring the whole tracksview thing we did before
and make the selections work directly on charts. We can probably use the
same thing w/ a GtkOverlay and custom positioning to replace the old
usage too.

src/sysprof/meson.build

@@ -15,6 +15,7 @@ sysprof_sources = [
   'sysprof-section.c',
   'sysprof-sidebar.c',
   'sysprof-single-model.c',
+  'sysprof-time-scrubber.c',
   'sysprof-traceables-utility.c',
   'sysprof-window.c',
 ]