Remove use of unsupported API i.e. LoginNewDevIdAsync() in AddWidget flow

[ssparach]

Dev Home version

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Windows build number

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Other software

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Steps to reproduce the bug

The "Add Widget" dialog currently uses the API as it immediately launches the browser upon Sign In.

To synchronize the login experience, the ask is for additional consumers of this API to replace the API usage by embedding the AdaptiveCard instead.

The desired user flow is:
Dashboard -> Add Widget -> Show AdaptiveCard instead of Sign In button redirecting to browser

Expected result

Actual result

Dashboard -> Add Widget -> Sign In -> Launches Browser

Included System Information

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