Escalate deprecation of Bluetooth.availability

[twyatt]

Note

Medium Risk
Intentional breaking API change: consumers still on Bluetooth.availability must migrate before upgrading, and the property no longer reports radio state on any target.

Overview
Escalates the planned removal of Bluetooth.availability by setting DeprecationLevel.ERROR on Bluetooth.availability, Availability, and platform Reason types (Android, Apple, JVM; web Reason entries were already deprecated without ERROR on the enum shell).

Removes all platform bluetoothAvailability implementations—Android adapter/location flows, Apple CBCentralManager state mapping, JVM flowOf(Available), and Web availabilitychanged listeners—and drops the expect val bluetoothAvailability from common code.

Bluetooth.availability is no longer a real Flow; its getter throws error("Deprecated"), so any remaining use fails at compile time (ERROR) or immediately at runtime if accessed.

^{Reviewed by Cursor Bugbot for commit 4df0a21. Configure here.}