Replace PlatformServices with AppContext

Proprietary

Replaces Microsoft.Extensions.PlatformAbstractions.PlatformServices.Default.Application.ApplicationBasePath with System.AppContext.BaseDirectory. The PlatformAbstractions package was removed in .NET Core 3.0. Also removes the obsolete using directive.

OpenRewrite.Recipes.CSharp.Migration.Dotnet.Net3_0.UsePlatformAbstractionsReplacement
mod run . --recipe=OpenRewrite.Recipes.CSharp.Migration.Dotnet.Net3_0.UsePlatformAbstractionsReplacement

Install it once, then run it on every repository under the current directory. New to the Moderne CLI? Set it up.