Custom fragment shader widget example for iced

A minimalistic example of making iced custom shader widget draw its contents using just a fragment shader. This provides reasonably fast access to writing arbitrary pixels into widget's canvas, something that iced custom canvas widget struggles with.

This example consists of:

• Iced boilerplate code for creating, updating, and drawing custom shader widget.
• Wgpu pipeline creation for a simple single-triangle pipeline without any buffers for vertex data.
• Wgsl shader file including both vertex and fragment shader code.
  • vertex shader generates 3 vertices coordinates based on vertex_index to make a triangle that fills the entire viewport.
  • fragment shader draws a pannable/zoomable mandelbrot set as a trivial example
• Mouse event handling that updates widget state. This state is then passed into the shader as uniform data.