Fixes legacy media business logic to return null when calling ToXml if the media item is trashed - this makes it consistent with how content works and also prevents being able to show the media on the front-end when it is trashed. Fixes up how the MediaService rebuilds the XML to make sure it's transactional based. Fixes: U4-3820 cached media xml is not cleared from the cmsContentXml table when recycled

Conflicts:
	src/Umbraco.Web/umbraco.presentation/library.cs