Modes tile & dialog a11y adjustments

Using a11y type button (instead of switch) to better represent how the
tile works. In the same vein, also moved away from using BooleanState
since it wasn't entirely accurate.

For the tiles in the dialog, the content description is already accurate
without any customization needed, so I removed that extra field.

Bug: 346519570
Test: manually tested with TalkBack, no major changes
Flag: android.app.modes_ui
Change-Id: I674db920b1b7d38711ec58448d5fa63821f8b513