Handle old migrations with 32-bit identity seed values

[ajcvickers]

From reported #24840 (comment) by @schuettecarsten

When using "Add-Migration" in Package Manager Console, I still get an exception:

System.InvalidCastException: Unable to cast object of type 'System.Int32' to type 'System.Nullable`1[System.Int64]'.
   at Microsoft.EntityFrameworkCore.SqlServerPropertyExtensions.GetIdentitySeed(IReadOnlyProperty property, StoreObjectIdentifier& storeObject) in Microsoft.EntityFrameworkCore.SqlServer.dll:token 0x6000160+0x22
   at Microsoft.EntityFrameworkCore.SqlServer.Metadata.Internal.SqlServerAnnotationProvider.For(IColumn column, Boolean designTime)+MoveNext() in Microsoft.EntityFrameworkCore.SqlServer.dll:token 0x6000494+0xe3
   at Microsoft.EntityFrameworkCore.Infrastructure.AnnotatableBase.AddAnnotations(AnnotatableBase annotatable, IEnumerable`1 annotations) in Microsoft.EntityFrameworkCore.dll:token 0x6001a0f+0x23
[...]

Okay, this was caused by my existing migrations. I had to replace all .HasAnnotation("SqlServer:IdentitySeed", 1) with .HasAnnotation("SqlServer:IdentitySeed", 1L). It would be great if efcore could handle existing migrations from previous versions.