For the first and last tab in a tab group, include the tab group's name in the accessibility description read by screen readers when the tab is in focus. As keyboard users go through the tab strip, the users will receive clues that they are passing into/out of a tab group.
This also reformats the tab tooltips in general.
Before:
```
$title $pid $active - $containerName
$audioPlaying
```
After:
```
$title
$pid $active
$tabGroupName - $containerName
$audioPlaying
```
For each portion of the tab tooltip string, parts of the string might not appear due to configuration (PIDs and active only shown with pref) or user state (container name only shown for a container tab, etc.) or UX choices (don't include the title in the accessibility description because screen readers already read out a tab's title by default)
Differential Revision: https://phabricator.services.mozilla.com/D245186
36e1885b72