Move grid-based Global Actions to power button when not using panel.

Use a pixel-value instead of a dp-value for defining location of the power button to ensure the menu appears in the correct place at different display sizes.
Improve separated list logic to avoid showing an empty separated list.
Switch ListGridLayout priority to minimize rows instead of columns.

Test: Automated tests pass. GA menu appears next to button when the panel is disabled (feature flag), and snaps to the bottom of the screen when the panel is enabled.
Change-Id: Ic0246dc4a2af7679e65c71ae8d9db758aeb9a3a8

Fixes: 127740041