Guidance panel in layout.json

[xshenwork]

What does this PR do?

• Add lint and editor support for GuidancePanel object in layout schema
• Add schema-based validation and tests for guidance panel properties
• Add code-completion, default snippets, and hover text on guidance panel json fields and tests
• Refactor backgroundImage to be used by regular panel and guidance panel
• Add support for linkbox item in regular panel items and groupbox items as well as tests

These are all only available in Winter '24 release.

What issues does this PR fix or reference?

@W-13900452