Make All Generated Classes internal

[brminnick]

Description of Change

This PR changes generated classes, i.e. code generated by TextAlignmentExtensionsGenerator, from public to internal.

The bug in #158 is caused by two matching public classes being generated in both the .NET MAUI library (eg net7.0-ios) and the referenced class library (e.g. net7.0).

📦MyMauiSolution
 ┣ 📂MyMauiApp
    - <TargetFrameworks>net7.0-android;net7.0-ios;net7.0-maccatalyst</TargetFrameworks>
 ┗ 📂MyLibrary
    - <TargetFramework>net7.0</TargetFramework>

Linked Issues

• Fixes [BUG] Source generator error - The call is ambiguous between the following methods or properties - CommunityToolkit.Maui.Markup.TextAlignmentExtensions #158

PR Checklist

• Has a linked Issue, and the Issue has been approved(bug) or Championed (feature/proposal)
• Has tests (if omitted, state reason in description)
• Has samples (if omitted, state reason in description)
• Rebased on top of main at time of PR
• Changes adhere to coding standard

Additional information

This aligns with a similar discussion on the CommunityToolkit.Maui repo: CommunityToolkit/Maui#756 (comment)

[brminnick]

NuGet Package Generated by this PR: https://dev.azure.com/dotnet/696bc9fd-f160-4e97-a1bd-7cbbb3b58f66/_apis/build/builds/83337/artifacts?artifactName=nuget&api-version=7.0&%24format=zip