fix example mesh2d_manual in wasm/webgl2

[mockersf]

Objective

• Example mesh2d_manual crashes in wasm/webgl2, as reported in Bevy Example panicked bevy-website#1123 (comment)

wgpu error: Validation Error

Caused by:
    In a RenderPass
      note: encoder = `<CommandBuffer-(0, 1, Gl)>`
    In a set_push_constant command
    Provided push constant is for stage(s) ShaderStages(VERTEX), however the pipeline layout has no push constant range for the stage(s) ShaderStages(VERTEX)

Solution

• Properly declare the push constant as in

  bevy/crates/bevy_sprite/src/mesh2d/mesh.rs

  Lines 514 to 524 in 4508077

  	let mut push_constant_ranges = Vec::with_capacity(1);
  	if cfg!(all(
  	feature = "webgl",
  	target_arch = "wasm32",
  	not(feature = "webgpu")
  	)) {
  	push_constant_ranges.push(PushConstantRange {
  	stages: ShaderStages::VERTEX,
  	range: 0..4,
  	});
  	}