Fix size and color of priority modes icons in status bar

* Allow StatusBarIcons to specify whether they want a "fixed" size instead of the variable width they normally have. This also affects their scaling calculations. This is mostly for app-provided icons which may have nonstandard sizes and proportions.
* Create a new drawable from constant state so that theming isn't shared with the other usages.

Additionally: Add a flow to ZenModeInteractor with the main active mode name and icon exclusively. While the QS tile cares about which other modes are active, neither status bar nor Smartspace do, which means we can use a flow that doesn't emit when more modes are activated (and thus avoid wasted work).

Bug: 360399800
Test: coming
Flag: android.app.modes_ui
Change-Id: I6a17d5a49f76169f15efc89432e1ce0f993d040e