Implement Pomelo specific test for upstream EF Core fix `The order of ExecuteUpdate setters is not preserved #35361`

[lauxjpn]

See dotnet/efcore#35361 (comment) upstream.

The fix is part of the EF Core 10 release train.

The test should verify that #1776 has been fixed by EF Core upstream.

[yykkibbb]

Hi @lauxjpn! I'm going to work on this issue and open a PR.

I'll add the test in NorthwindBulkUpdatesMySqlTest using the code @roji suggested in the upstream comment.

Plan:

• Add Update_Where_set_ordering_is_preserved test method to NorthwindBulkUpdatesMySqlTest.cs
• Use TestHelpers.ExecuteWithStrategyInTransactionAsync to verify that MySQL's left-to-right SET clause evaluation produces correct results when setter order is preserved
• Add using Microsoft.EntityFrameworkCore; for ExecuteUpdateAsync / CountAsync extension methods

[yykkibbb]

Opened a PR: #2034. Please take a look when you get a chance!