title: ActionContext in IActionContextAccessor registered through DI is null
body: <p>I'm having some issue with <code>IActionContextAccessor</code> using asp.net core's builtin DI container. The <code>IActionContextAccessor.ActionContext</code> property is null on every request. I'm trying to register <code>IActionContextAccessor</code> like this:</p>
  
  <pre><code>services.TryAddSingleton&lt;IActionContextAccessor, ActionContextAccessor&gt;( );
  services.TryAddScoped&lt;ITenantProvider, TenantProvider&gt;( );
  </code></pre>
  
  <p><br/>
  And I'm trying to access the <code>ActionContextAccessor.ActionContext</code> here</p>
  
  <pre><code>public TenantProvider( SomeTenantsDbContext context, IActionContextAccessor accessor )
  {
      var alias = accessor?.ActionContext?.RouteData?.Values["tenant"]?.ToString();
      if(alias != null)
      {
          _tenantId = context.Tenants.FirstOrDefault( t =&gt; t.Alias == alias )?.Id;
      }
  }
  </code></pre>
  
  <p><br/>
  What could be the cause for this. All suggestions are welcome</p>