Clean up namespaces generated by extract to code-behind gesture

[danroth27]

You get a lot of namespaces when you use the extract to code-behind gesture:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Components;
using System.Net.Http;
using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.Components.Authorization;
using Microsoft.AspNetCore.Components.Forms;
using Microsoft.AspNetCore.Components.Routing;
using Microsoft.AspNetCore.Components.Web;
using Microsoft.AspNetCore.Components.Web.Virtualization;
using Microsoft.JSInterop;
using BlazorApp53;
using BlazorApp53.Shared;

namespace BlazorApp53.Pages
{
    public partial class Counter
    {
        private int currentCount = 0;
        private void IncrementCount()
        {
            currentCount++;
        }
    }
}

Can we clean these up to only the required ones?

[davidwengier]

When I do this, I also get global:: aliases on most of the using declarations. We should remove them too, they're an implementation detail of the generated C# from the Razor compiler.