Upgrade to Orchard Core 3.0 and .NET 10 (OSOE-925)

[Piedone]

...once it's released.

• Keep https://devblogs.microsoft.com/dotnet/performance-improvements-in-net-9/ in mind. In particular, use System.Threading.Lock where appropriate. Also see https://maoni0.medium.com/preparing-for-the-net-10-gc-88718b261ef2 (e.g., DATAS is now enabled by default).
• Swagger is now gone so the features using it in the UI Testing Toolbox need to be adapted. Also see this post.
• Change all sync-over-async site settings accesses like this to use the new sync GetSiteSettings method from Preload site settings on tenant activation OrchardCMS/OrchardCore#17798.
• In UITT remove Lombiq.Tests.UI.Helpers.AppLogAssertionHelper.NotMediaCacheEntries, as it's no longer needed since Prevent unnecessary exception "Error deleting cache folder ..." when the folder doesn't exist OrchardCMS/OrchardCore#18341 was merged.
• Remove System.Linq.Async package references, since that's now part of .NET.

Jira issue