Smoother flow when choosing between this or other device

[PeterOrneholm]

Is your feature request related to a problem? Please describe.
BankID have gathered a few best practises around how to implement the flow. See:
https://www.bankid.com/utvecklare/guider/praxis

Most relevant for us would be:
https://www.bankid.com/utvecklare/guider/praxis/praxis-dator-mobil

We should implement this view:

The idea is to optimize for the most likely flow using only one initial button.

• Detect if the user is on a mobile device or desktop:
  • On desktop: Show the animated QR-code and below that a button/link that allows to launch on the same device
  • On mobile: Here there is no clear recommendation on the link above, but I've tried their test on https://test.bankid.com/ and then it behaves like this: Show a text and a button to launch the BankID app. Below that, show a link to switch to BankID on another device.
    

What area is it related to

• UI

Describe the solution you'd like
Right now we register BankID on the same device and BankID on another device as two separate schemes in ASP.NET. It's clear that it would be better to just have one registration and that Active Login would display the most optimal UI out of this. We probably should allow for an option to disable desktop/mobile if that is a requirement.

The simplest setup would end up being this:

services
    .AddBankId(bankId =>
    {
        bankId.UseSimulatedEnvironment();
    });
    
services
    .AddAuthentication()
    .AddBankIdAuth();

Additional context
Always showing the launch button will ensure we have a user interaction when launching BankID.

A few things that could/should be done together with this:

• Refactor frontend code Refactor frontend code #162
• Automatically set policy on Other Device Automatically set policy on Other Device #365
• Avoid browser detection for app launch Avoid browser detection for app launch #264
• Hide QR code once it's scanned Hide QR code once it's scanned #274
• Allow for easier usage of BankIdClient when used without the ASP.NET Core pipeline Allow for easier usage of BankIdClient when used without the ASP.NET Core pipeline #235