Home screen on gallery needs improved a11y navigation

[guidezpl]

Acceptance Criteria

• Swipe traversal works in a sensible way
• The "crane" section is reachable via a11y navigation
• Expanding buttons/menus does not disrupt other lists/make announcements about being in a new list of more items than actually available.

Reproduction steps

Run the gallery on a physical Android device with Talkback enabled. Start swiping left/right to navigate around. Note:

• Cards for demos don't scroll when activated
• Cannot reach the Crane item at all
• Expanding any of the buttons along the bottom announces in a list of 6 items
• Swiping beyond those items leads to an invisible list (I think it's the menu list?)

/cc @willlarche @goderbauer @rami-a @darrenaustin @vick08

Migrated from material-components/material-components-flutter-gallery#134

[guidezpl]

Next step is to integrate change from flutter/flutter#45598

[guidezpl]

Verified that the issues raised above are fixed. Found 2 remaining issues

• There are 2-3 unnecessary (and unannounced) items when opening the settings. Should go Close button → Text scaling → ...
• There is an unnecessary (and unannounced) item after the "Settings (button)" item on the home page