Prevent modes dialog from updating on theme change

This is a workaround necessary because the background of the dialog
(which we don't control) does not get updated when the theme changes.
Since the composables do update, this leads to showing things like white
text on a white background, which is especially bad since bedtime mode
by default turns on dark theme when activated.

Note that this only works if the composables use
MaterialTheme.colorScheme to get the colors, so I had to update some
components to use that instead of LocalAndroidColorScheme. However, the
documentation of AndroidColorScheme points out that we should use
MaterialTheme.colorScheme whenever possible instead, so this change
should be safe (although unflagged). The dialog itself is flagged behind
modes_ui.

Fix: 364528021
Test: manually tested that toggling a mode that changes the theme
doesn't make the dialog unreadable
Flag: android.app.modes_ui
Flag: EXEMPT trivial compose change

Change-Id: I02f9868a210b1d8d7f57f89d35d8178acccd0e47