Clarify documentation of RefreshSignInAsync (#10637)
Clarify documentation of RefreshSignInAsync (#10637)

Helps to address issues of confusion raised in https://github.com/aspnet/Identity/issues/1900 and https://github.com/aspnet/AspNetCore/issues/5844
aspnet/AspNetCore,aspnet/AspNetCore,aspnet/AspNetCore,aspnet/AspNetCore,aspnet/AspNetCore,aspnet/AspNetCore,aspnet/AspNetCore,aspnet/AspNetCore,aspnet/AspNetCore