Enable RemoteGrouping by default for EFCore >= 2.2

[AlekseyMartynov]

When 2.1 is released, we need to reconsider this:

DevExtreme.AspNet.Data/net/DevExtreme.AspNet.Data/DataSourceLoaderImpl.cs

Lines 27 to 29 in 535e1ea

	// Until https://github.com/aspnet/EntityFramework/issues/2341 is implemented
	// local grouping is more efficient for EF Core
	var preferLocalGrouping = Compat.IsEFCore(source.Provider);

[AlekseyMartynov]

Checklist:

• Add test project for EF Core 2.1 (Reorganize test projects #238)
• Fix Interval grouping by a nullable number throws #239
• Group by an empty key with an aggregate throws 'must be reducible node' dotnet/efcore#11905 (expect in 2.1.0)
• GroupBy constant and element selector produces invalid SQL dotnet/efcore#11993 (expect in 2.1.1)
• Add grouping stress test
• Query: consider expanding null safety beyond nav rewrite dotnet/efcore#12284
• Query: Sum should return zero for empty collections regardless of the type dotnet/efcore#800, Feature toggle for empty Sum equal zero? dotnet/efcore#12307
• Use stable EF Core 2.1 in Sample
• AVG is evaluated locally, Query: GroupBy Where Aggregate translation to server dotnet/efcore#11711
• Specific GroupBy + Sum is evaluated locally dotnet/efcore#12433 / Query: GroupBy aggregate failure when key property is also part of Elementselector dotnet/efcore#11999 (expect in 2.2.0)