Center glanceable hub widgets vertically in the window

Adjust grid padding and gutter values for compact screen sizes in
portrait and landscape orientation.

In CommunalContent, center communal grid vertically in window using
even top and bottom margins.

Bug: b/399688758
Test: on foldable and tablet
Flag: com.android.systemui.communal_responsive_grid
Change-Id: I3949d39b867b5bce1f0f6e42ac0c55bf40160941