Important changes for UWP apps

Upgrade the minimum target platform to 10.0.17763.0.
Upgrade Microsoft.NETCore.UniversalWindowsPlatform to 6.1.9 or above.
Add a reference to Microsoft.IdentityModel.Abstractions, for projects that use package.json.

New Features

Logs are now consistent when you use several .NET authentication libraries from Microsoft. See 3028.
Exposed tenant ID and scopes in TokenCacheNotificationArgs. See 3389.
Added new WithClientAssertion API that exposes the token endpoint. See 3352.
Added additional descriptive information to error logs. See 3278.
Updated support from .NET Standard 1.3 to.NET Standard 2.0. See 1991.

Bug Fixes

Tenant profiles are now returned when calling GetAccounts with broker enabled. See 3349.
Fixed parsing of authentication result from broker preview. See 3354.
Fixed DSTS endpoints. See 3492.
Privacy and Terms of Use links are now visible in embedded picker UI on smaller screens. See 3153.
Fixed broker Proof-of-Possession token appearing as Bearer when calling GetAuthorizationHeader(). See 3353.
Ensured MSAL doesn't check local cache for tokens when using Proof-of-Possession with the broker preview. See 3363.