Improve Error Message: Resolving unregistered service from internal service provider

[rowanmiller]

Currently we assume that resolving an unregistered service means you haven't configured a provider:

No database provider has been configured for this DbContext. A provider can be configured by overriding the DbContext.OnConfiguring method or by using AddDbContext on the application service provider. If AddDbContext is used, then also ensure that your DbContext type accepts a DbContextOptions object in its constructor and passes it to the base constructor for DbContext.

But it is particularly confusing if you try to resolve a context from the internal service provider (not a super weird thing to assume might work):

public static void MyExtensionMethod<TEntity>(this DbSet<TEntity> set)
{
    var context = set.GetService<DbContext>();
}

We should update the message so say something like "Could not resolve '', this may be because...".