Fix Clock. Tooltip calendar text overflows(#2240)

[LukashonakV]

Hi @Alexays, @FilippoBonazziSUSE this MR solves #2240 Actually here it's GtkLabel wrong behavior with tooltips. Even @BrianCArnold has found workaround it's better to have code fixed. Temporary for now I replaced clock label with Gtk::TextView. In order to have the same styling as it was for tooltips in the system, users should use next css styling

textview#clock.tooltip, textview#clock.tooltip text {
   background-color: inherit;
   padding: inherit;
}

For now I'm trying to write test case in pure C in order to provide it gtk maintainers to fix gtk

So fixed variant looks good