Ported Markdown Preview to DevToys 2.0

[veler]

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• New feature or enhancement
• UI change (please include screenshot!)
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Internationalization and localization
• Other (please describe):

What is the current behavior?

DevToys 2.0 doesn't have a Markdown Preview tool yet.

What is the new behavior?

• Ported the Markdown Preview tool.
• [New in DevToys 2.0] Images are now displayed when the Markdown has the full URL. DevToys 1.0 couldn't because it couldn't access to internet at all. Images In Markdown #972
• [New in DevToys 2.0] Syntax highlighting. Add code block syntax highlighting to the markdown editor #255
• [New in DevToys 2.0] Yaml Front Matter support. Make Markdown Preview render Front matters #733
• I needed to add a IUIWebView, which in is mocked through an iframe in HTML.

Other information

Quality check

Before creating this PR:

• Did you follow the code style guideline as described in CONTRIBUTING.md
• Did you build the app and test your changes?
• Did you check for accessibility? On Windows, you can use Accessibility Insights for this.
• Did you verify that the change work in Release build configuration
• Did you verify that all unit tests pass
• If necessary and if possible, did you verify your changes on:
  • Windows
  • macOS (DevToys 2.0)
  • Linux (DevToys 2.0)