Add default icons for all mode types

Also a couple of icon-related fixes:
* Use the proper context, since we need theming (this also means it cannot be stored in IconLoader, which is a singleton, and must be supplied).
* Force apply the standard size and tint, since app-provided icons may be arbitrary.
* Fix the schedule-time icon (the viewport size was incorrect).

Bug: 308819461
Fixes: 333528437
Flag: android.app.modes_ui
Test: atest com.android.settings.notification.modes
Change-Id: Iae447c8c4a0218a8bc989c01d1d56d0c06abd8e7