Add [GeneratedCode] and [ExcludeFromCodeCoverage] Attributes to SourceGenerators

[brminnick]

Description of Change

This PR adds the following attributes to TextColorToGenerator:

[global::System.CodeDom.Compiler.GeneratedCode("{{className}}", "{{assemblyVersion}}")]
[global::System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]

Linked Issues

• Fixes Generated code is not marked with GeneratedCodeAttribute Maui#1467

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

The GeneratedCodeAttribute class can be used by code analysis tools to identify computer-generated code, and to provide an analysis based on the tool and the version of the tool that generated the code.