V13: Clear username cache

[Zeegaan]

Notes

• There was a bug where you could still login as a member for a little while, after you've deleted the member.
  This was caused by the userNameCache not being cleared in the member repository.
• Clears the user name cache in the MemberRepository when members are updated/deleted

How to test

• Create RegisterMember.cshtml partial view from snippet
• Create Login.cshtml partial view from snippet
• Create LoginStatus.cshtml partial view from snippet
• Create a doc type ContentPage and in its template add:

@using Umbraco.Cms.Web.Common.PublishedModels;
@using Umbraco.Cms.Core.Services;
@inherits Umbraco.Cms.Web.Common.Views.UmbracoViewPage<ContentModels.ContentPage>
@inject IMemberService MemberService
@using ContentModels = Umbraco.Cms.Web.Common.PublishedModels;
@{
	Layout = null;
	var isLoggedIn = Context.User?.Identity?.IsAuthenticated ?? false;
}

@if (!isLoggedIn)
{
    @await Html.PartialAsync("RegisterMember")
    <hr/>
    <br/>
    @await Html.PartialAsync("Login")
}
else
{
    @await Html.PartialAsync("LoginStatus")
}

• Register a member
• Logout
• Delete the member
• Try to login ---> This should fail