Add more locations and sizes for system bezel notification

Currently, both `BezelLocation` and `BezelSize` have only a `.normal` position and size, which mimics that of the system bezel notifications. More options should be provided, and perhaps `.normal` location should become an alias to one like `.bottomCenter`.

Locate the BezelLocation and BezelSize definitions and inspect how their .normal values are used for system bezel notifications. Determine suitable additional locations and sizes, decide whether .normal should alias .bottomCenter, and verify that existing notification behavior remains unchanged.

Written by the indexing model from the issue text.