Add custom actions to improve Voice Access swipe on UMO in hub

When using "number" command, Voice Access speech recognition may
misinterpret non-fluent user input and outputs an unintended swipe
start position. This leads to scrolling of the entire hub instead
of the UMO, as the hub is horizontally scrollable.

This fix adds custom actions to enable reliable control of
switching players in UMO on hub, via the "show commands" voice
command.

Fixes: 378805659
Flag: EXEMPT bugfix
Test: atest MediaCarouselScrollHandlerTest
Test: manually with VoiceAccess
Change-Id: Id433d14652b54311c1bb63305574c6d961020d75