Rewrite WebGL rendering modules without wasm-bindgen

[nat-rix]

• [x] context initialization
  • [x] vertex array buffer
  • [x] compile shaders
  • [x] fetch shaders
  • [x] initialize framebuffer and renderbuffer
    • [x] create pixel effect
• [x] texture api
  • [x] force textures to RGBA-format
  • [x] perform texture packing
  • [x] uploading
  • [x] unloading
• [x] correct canvas and viewport size handling
• [x] shader rewrite for texture atlas rendering
• [x] instanced drawing
• [x] final cleanup
• [x] write comments

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Changes in this PR shall also include some optimizations and a better implementation. For example the glBlitFramebuffer-function will be used instead of the 2-render-passes system.

[nat-rix]

When reviewed, "shader rewrite for texture atlas rendering" can be checked :P