Use fully qualified namespace for Colors reference in TextToColorGenerator

[IIARROWS]

This change should prevent "ambiguous reference" error to occur when other packages are included in a MAUI project that provide their own Color objects.

Examples of such libraries is MudBlazor.

Description of Change

In the source code generator use a fully qualified namespace to the Color object, so Color is changed into global::Microsoft.Maui.Graphics.Colors following the example for the similar solution for of #1331

As per previous PR, no tests added, current tests are sufficient to cover this change (and using the wrong value fail).

Linked Issues

• Fixes [BUG] Ambiguous reference error occurs when other package is included that provides its own Colors object #1535

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
• Documentation created or updated: https://github.com/MicrosoftDocs/CommunityToolkit/pulls

Additional information

[IIARROWS]

@dotnet-policy-service agree