fix(#1271): tabpanel should be labelled by the Picker button element when Tabs are collapsed (#1272)
* fix(#1271): tabpanel should be labelled by the Picker button element when Tabs are collapsed
The aria-labelledby attribute on the tabpanel should be updated to refer to the Picker rather than the current tab, which is no longer in the DOM.
* fix(#1271): vertical orientation should not change aria-labelledby on tabpanel