Create CustomFont Interface

[froggomad]

PR Description: Add CustomFont Struct for Custom Font Creation and PageElement Extensions For Custom Font Management

Summary

This PR introduces a new struct, CustomFont, and extends PageElement to support custom font management, allowing developers to define, add, and use custom fonts easily.

Key Changes

1. CustomFont Struct:

   • Provides a way to define a custom font using a font family name and a URL string (which can be local or remote).
   • Adds optional fallback font families that are joined in CSS syntax, allowing for a smooth transition if the primary font fails to load.
   • Includes a computed property, fontURLString, which returns a valid URL string or an "Invalid URL" message if the URL is malformed.

2. PageElement Extensions:

   • addCustomFontFace(_:): Adds a CSS @font-face rule using the CustomFont instance to make the font available across the application.
   • useCustomFont(_:): Applies the custom font to elements, leveraging the fallback font stack if specified.

Example Usage

The PR provides an example for usage with an enum, BrandFont, that returns predefined CustomFont instances. The example demonstrates adding the custom font faces to the HTML and using a specific font as a default on the Body element.

Additional Notes

• This setup supports local and remote font resources by specifying a valid URL.
• The structured approach ensures that custom fonts are consistently referenced, providing flexibility with fallback options and easy integration into different parts of the project.

Benefits

• Enhances the styling capabilities by making font integration more straightforward and scalable.
• Improves code readability and reuse by centralizing font management.

Testing

• Ensure custom fonts load correctly in various browsers and environments (local/remote fonts).
• Verify fallback behavior by disabling network access to test fallback font rendering.

[twostraws]

Hello! Thank you for this contribution – I think it's an important step forward. I'm going to merge it in now, but I want to find some time to noodle around with the API a little more to see if we can make it a little more transparent in use.