Prefer equality when comparing values

Most databases can take advantage of indexes (and in some cases even auto-generate them) when queries perform equality comparisons (instead of inequality).

In some places EFCore already tries to lean towards equality https://github.com/dotnet/efcore/blob/20edb631265527a73cb9b9ab474cd0484c49a771/src/EFCore.Relational/Query/SqlExpressionFactory.cs#L657-L666

In other places it disregards this and in fact can even replace equality comparisons with inequalities https://github.com/dotnet/efcore/blob/20edb631265527a73cb9b9ab474cd0484c49a771/src/EFCore.Relational/Query/SqlNullabilityProcessor.cs#L1748-L1757 https://github.com/dotnet/efcore/blob/20edb631265527a73cb9b9ab474cd0484c49a771/src/EFCore.Relational/Query/SqlNullabilityProcessor.cs#L1803-L1804

It would be better to avoid converting equalities into inequalities and, when possible, convert inequalities into equalities.