Allow changing image aspect in AvatarView

[MahmoudAlEssawi]

Add Aspect property with ImageSource Aspect enumeration to AvatarView

[GeorgeLeithead]

@MahmoudAlEssawi I don't see any reason why we couldn't provide the ability to set the Aspect of the AvatarView. It MAY cause issues when used in conjuction with a border. It should be reasonably easy to implement, as currently we default the aspect to AspectFill.

Before spending time on this, can I ask what the reason for needing aspect is specifically?

[CliffAgius]

Closed as per the Community Stand-up discussion here: https://youtu.be/N9wMcBP4jtg?t=2889 where it was agreed that New Features need to get above 7 upvotes within 6 months to progress to being reviewed by the maintainers.