panel: Rework panel layout, and refactoring

I reworked the layout of the panel, so that the clock is on the left, and all of the widgets are on the right side. I think this will be a much easier layout to work with for a broader amount of devices, especially for dealing with notches and punch-hole cameras.

I moved the text for the mobile data, and added the date display into the quicksettings panel, since they are longer labels and aren't necessary to be shown at all times.

I did some refactoring of IndicatorsRow, fixing the issue where tray icons overlap the mobile data icon, and using a layout instead of anchors everywhere.

These changes also had to be applied to the lockscreen header bar, where I replaced the clock display and with the mobile data text (since the clock is already shown).

Private API was also added to expose the top panel height so that the task panel doesn't have to hardcode it.