fix: Fix TextBox.Foreground on Skia

[Youssef1313]

GitHub Issue (If applicable): closes #7172

PR Type

What kind of change does this PR introduce?

• Bugfix

What is the current behavior?

• On Skia, we update Foreground only for the DisplayBlock (appears only when unfocused)
• On Skia WPF, we only support SolidColorBrush

What is the new behavior?

• Update Foreground properly for both the input widget and the DisplayBlock.
• Support more brushes on WPF.

PR Checklist

Please check if your PR fulfills the following requirements:

• Docs have been added/updated which fit documentation template (for bug fixes / features)
• Unit Tests and/or UI Tests for the changes have been added (for bug fixes / features) (if applicable)
• Validated PR Screenshots Compare Test Run results.
• Contains NO breaking changes
• Associated with an issue (GitHub or internal) and uses the automatic close keywords.
• Commits must be following the Conventional Commits specification.

Other information

Internal Issue (If applicable):

[gitpod-io]

[jeromelaban]

Thanks for your contribution!