Added Base64 Image Encoder / Decoder

[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?

Missing Base64 Image Encoder / Decoder in DevToys 2.0

What is the new behavior?

• Added Base64 Image Encoder / Decoder
• Added IUIImageViewer element
• Refactored the PickedFile class and renamed it to SandboxedFileReader
• Added support for self-cleaning temp files in IFileStorage.

REMAINS TO DO

• Base64 Image Encoder / Decoder CLI tool
• Unit tests

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)