ImageCache to clean dictionary instead of keeping semaphores permanently in memory

[MarkCiliaVincenti]

Description

https://github.com/dotnet/maui/blob/main/src/Controls/src/Core/LockingSemaphore.cs looks to be unreferenced and can be deleted.

ImageCache has a different implementation at https://github.com/dotnet/maui/blob/main/src/Compatibility/Core/src/Android/ImageCache.cs however the implementation as is keeps filling up a ConcurrentDictionary with semaphores per image name which are then never cleaned from memory.

Public API Changes

I am the author of a popular library called AsyncKeyedLock at https://github.com/MarkCiliaVincenti/AsyncKeyedLock and can propose changes to ImageCache to make use of this library which can clean up behind it with negligible performance difference.

Intended Use-Case

ImageCache.