[Workspaces] Move to WPF Fluent and tweak overall UX

[niels9001]

Summary of the Pull Request

This PR includes the following changes:

• Remove the dependency of ControlzEx and ModernWpf, and instead uses the default WPF Fluent theming. No more third-party packages.
• A lot of UI design refinements: using the proper fontweights, spacing, Mica background, and default Fluent styles.
• Usability improvements: action buttons are at the top, full width scrolling.

Related: #46220

PR Checklist

• Closes: #xxx

• Communication: I've discussed this with core contributors already. If the work hasn't been agreed, this work might be rejected
• Tests: Added/updated and all pass
• Localization: All end-user-facing strings can be localized
• Dev docs: Added/updated
• New binaries: Added on the required places
  • JSON for signing for new binaries
  • WXS for installer for new binaries and localization folder
  • YML for CI pipeline for new test projects
  • YML for signed pipeline
• Documentation updated: If checked, please file a pull request on our docs repo and link it here: #xxx

Detailed Description of the Pull Request / Additional comments

Validation Steps Performed

[crutkas]

What is the space savings.