Add WebGL shader support to web frontend

[joamag]

Summary

• add WebGL shader renderer in web frontend
• hook shader parameter in frontend to initialize WebGL
• copy shaders from SDL frontend
• document shader support in changelog

Testing

• cargo fmt --all
• cargo clippy --fix --allow-dirty --allow-staged --all-features --all-targets
• black .
• cargo test --all-targets --features simd,debug,python

---

https://chatgpt.com/codex/tasks/task_e_684dbe78e5748328a39044ddde8b59cf

Summary by CodeRabbit

• New Features
  • Introduced support for Web frontend shader effects using WebGL, enabling enhanced visual rendering options in the web environment.
  • Added multiple built-in shader options, including bilinear, smooth bilinear, CRT, passthrough, and master shaders with frame blending.
  • Enabled frame blending and advanced scaling effects for improved image quality in the web frontend.
  • Added dynamic shader selection via URL parameter for customizable visual effects.