refs #17129. Fix some accessibility issues:

1/ move button role to element that has title attribute so VoiceOver announces button title. Also move aria-grabbed to button element.
2/ The Dojo mobile ComboBox widget is missing an aria-expanded. The combobox must have aria-expanded=true if the list is displayed or aria-expanded=false when it is not.

Thanks David Tood (IBM, CCLA).