feat(style): add support for custom gradient fills

[charles4221]

Closes #368

Summary

• Correctly supports the fill prop by ensuring it is applied to the svg element while also removing any built-in fill props from nested path elements so the svg fill takes precedence
• Adds new props for linearGradient and radialGradient to allow easy application of gradients to icons without providing custom fill and creating the gradient elements yourself elsewhere in the DOM

Result

	Code Sample	Result
Linear Gradient
Radial Gradient

[Copilot]

Pull request overview

Adds first-class support for custom fill values (including url(#...) gradient references) in the React FontAwesome icon rendering pipeline, and introduces convenience props to generate inline SVG gradient definitions.

Changes:

• Adds linearGradient and radialGradient props to FontAwesomeIconProps.
• Updates the SVG abstract-element converter to (a) strip built-in fill attributes from child paths when an overriding fill/gradient is provided and (b) optionally inject gradient elements + apply fill="url(#id)" at the <svg> level.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 7 comments.

File	Description
src/types/icon-props.ts	Defines new gradient prop types and inline docs for consumers.
src/converter.ts	Implements fill-override behavior and gradient element injection during abstract-to-React conversion.

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

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[charles4221]

@robmadole this is now ready, would love to get your eyes over it when you get a sec!