[Accessiblity] Set aria-current for manage nav

[HaoK]

Fix for https://devdiv.visualstudio.com/DevDiv/_workitems/edit/1411043/

Adds area-current="page" on the currently selected nav item for the manage nav bar

Example html of when the change password is selected, null attributes are not rendered so its safe to attempt to set it on each item

<li class="nav-item"><a class="nav-link" id="profile" href="/Identity/Account/Manage">Profile</a></li>
 <li class="nav-item"><a class="nav-link" id="email" href="/Identity/Account/Manage/Email">Email</a></li>
 <li class="nav-item"><a class="nav-link active" id="change-password" aria-current="page" href="/Identity/Account/Manage/ChangePassword">Password</a></li>
  <li class="nav-item"><a class="nav-link" id="two-factor" href="/Identity/Account/Manage/TwoFactorAuthentication">Two-factor authentication</a></li>
  <li class="nav-item"><a class="nav-link" id="personal-data" href="/Identity/Account/Manage/PersonalData">Personal data</a></li>

[sebastienros]

Was javascript an option talked about? Or do accessibility attributes/classes need to be defined server-side?

[HaoK]

Is there a benefit/is it easier to using javascript, I just copied the pattern of the active attribute that was already doing something similar, but it was definitely a bit onerous

[HaoK]

/backport to release/6.0

[github-actions]

Started backporting to release/6.0: https://github.com/dotnet/aspnetcore/actions/runs/1306369041

[github-actions]

@HaoK an error occurred while backporting to release/6.0, please check the run log for details!

Error: @HaoK is not a repo collaborator, backporting is not allowed.