Add Dismiss action in Talkback Local Context Menu

- Add dismiss action for cards that can be dismissed.
- Remove importantForAccessibility from sliceView so Talkback can
recognise this view in order to generate Local Context Menu.

Fixes: 146910157
Test: Enable Talkback -> Move focus to removeable contextual card -> use
up-right gesture -> see Local Context Menu

Change-Id: I75a7394e94e6939d48cc379f62eab66f7903fd98