webcanvas: added FontProvider for pluggable font backends

[tinyjin]

• Remove FontRegistry to ensure ThorVG manages font loading status
• Added new beta API (TVG.setFontProvider) to set user own backend (default: fontsource)

API addtion & modification

// addition
+ Font.setProvider(provider: FontProvider): void

// modification (option parameter is decoupled from specific vendor)
- Font.load(name: string, options?: FontsourceOptions): Promise<void>
+ Font.load(name: string, options?: Record<string, unknown>): Promise<void>

Example

import { FontsourceProvider } from '@thorvg/webcanvas';

// Connect to own backend
TVG.Font.setProvider({
    fetch: async (name) => {
      const res = await fetch(`https://my-cdn.com/fonts/${name}.ttf`);
      return { data: new Uint8Array(await res.arrayBuffer()), type: 'ttf' };
    }
});

// Load from font provider
await TVG.Font.load('my-font');

// Reset to default provider
TVG.Font.setProvider(new FontsourceProvider());

issue: #242

[github-actions]

🚀 Playground preview deployment ready!

🎮 Playground: https://thorvg-playground-hw4nonix9-thorvg-web.vercel.app

[tinyjin]

TVG.Font.load API is necessarily called, not to make Text API (font) async call(Promise)

[Copilot]

Pull request overview

This PR introduces a pluggable FontProvider abstraction for @thorvg/webcanvas so Font.load() can auto-fetch font binaries via a configurable backend (defaulting to a new FontsourceProvider), and removes the old FontRegistry-based tracking.

Changes:

• Added FontProvider / FontProviderResult interfaces and a default FontsourceProvider implementation.
• Added Font.setProvider() and updated Font.load(name, options?) to use the configured provider (options now vendor-agnostic).
• Updated package exports/types accordingly and removed the old FontRegistry utility.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
packages/webcanvas/src/utils/FontRegistry.ts	Removed previous fontsource-fetch dedup/registry helper.
packages/webcanvas/src/core/FontProvider.ts	Added provider interface for pluggable font fetching backends.
packages/webcanvas/src/providers/FontsourceProvider.ts	Added default provider that fetches fonts from the fontsource CDN.
packages/webcanvas/src/core/Font.ts	Switched Font.load() to provider-based fetching and added Font.setProvider().
packages/webcanvas/src/index.ts	Exported the new provider/types and re-exported FontsourceOptions from the provider module.
packages/webcanvas/src/core/Text.ts	Minor JSDoc update for Text.font().

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[github-actions]

🚀 Playground preview deployment ready!

🎮 Playground: https://thorvg-playground-riha4e015-thorvg-web.vercel.app