fix(material/datepicker): use aria-live over cdkAriaLive on period button (#24398)
fix(material/datepicker): use aria-live over cdkAriaLive on period button (#24398)

On the period button on the calendar, use `aria-live` over `cdkAriaLive`
because that seems to work better with VoiceOver. This fixes an issue
where VoiceOver did not announce the month after clicking the "Month
Month"/"Previous Month" buttons (#24397).

Fixes #24397
crisbeto/material2,angular/components,crisbeto/material2,angular/components,angular/components,crisbeto/material2,crisbeto/material2,angular/components