Added experimental ghostscript wasm conversion using zero config

[ahnafnafee]

Experimental: Zero-Config Internal Rendering (WASM + SVG)

Summary

This draft PR introduces a major architectural shift to make the extension "Zero Config". It eliminates the requirement for users to manually install Ghostscript and Poppler by bundling a WebAssembly (WASM) version of Ghostscript and using pdf.js for client-side rendering.

Key Changes

• Internal Rendering: Replaced child_process calls to system binaries (ps2pdf, pdftocairo) with @jspawn/ghostscript-wasm.
• SVG-Based Preview: Switched from Canvas rendering to SVG rendering using pdf.js SVGGraphics.
• Enhanced Zoom/Pan: Integrated svg-pan-zoom for infinite, crisp vector zooming without pixelation.
• Scoped Backgrounds: Background color picker now applies only to the document "paper", preserving transparency logic.
• Configuration Removal: Removed all postscript-preview.path.* settings as they are no longer needed.
• Async Refactoring: Simplified extension.ts command handlers to avoid potential Marketplace flagging for long-running async activations.

Benefits

• Truly Zero Config: Users just install and run. No more "Ghostscript not found" errors.
• Consistent Rendering: Using a bundled engine ensuring identical output across Windows, macOS, and Linux.
• Better UX: Vector-based zoom allows for inspecting fine details in PostScript drawings.

Concerns & Open Questions

1. Extension Size (Critical)

The VSIX package size has increased from ~200KB to ~30MB.

• Cause: This is primarily due to bundling the ghostscript.wasm binary and its snapshot.
• Impact: Longer download/install times.
• Potential Solution: Implementing a "Download on Demand" strategy where the binary is fetched from a CDN on the first run, keeping the core extension small.

2. Startup Performance

Initializing the WASM environment might incur a slight startup penalty compared to spawning a native process, though subsequent operations should be fast.

3. Licensing

ghostscript-wasm is AGPL-licensed. While the extension logic is MIT, bundling AGPL components may have implications for distribution.

Testing

• Tested on Windows with various .ps and .eps files.
• Verified special characters in filenames are handled correctly.
• Confirmed svg-pan-zoom works with valid viewBox scaling.