Fix display settings persistence with LRU cache.

Rotation and density settings for external or simulated displays were
not being persisted across reboots. This was caused by an overly
aggressive cleanup mechanism that would remove settings for displays
that were only temporarily disconnected, such as during a device reboot.

This change replaces the ArrayMap in DisplayWindowSettingsProvider with
an LruCache to manage display settings. This aligns with the persistence
strategy used by DisplayManager's DisplayTopologyXmlStore, ensuring that
the settings for the 100 most recently used displays are retained.

When the cache limit is reached, the least recently used setting is
evicted. This prevents the settings file from growing indefinitely while
correctly preserving settings for active and recently used displays
across reboots. The previous removeStaleDisplaySettingsLocked method is
now obsolete and has been removed.

Bug: 397398590
Flag: EXEMPT bug fix
Test: atest WmTests:DisplayWindowSettingsProviderTests
Change-Id: I6bf2a0312403ebda10194bc76fe3e443d50f664b