Experimental wgpu WebGL backend support

- Added missing `draw_cache_align_4x4` call for `brush_glyph` on wasm32 target
- Added WebGL support to `integratio_wgpu` example
- Fixed test.yml CI workflow
- Removed spir-v shader in `integration_wgpu`; Fixed formatting
- Removed redundant `BoxStream` typedef

examples/integration_wgpu/src/shader/frag.wgsl

@@ -0,0 +1,4 @@
+[[stage(fragment)]]
+fn main() -> [[location(0)]] vec4<f32> {
+    return vec4<f32>(1.0, 0.0, 0.0, 1.0);
+}

examples/integration_wgpu/src/shader/vert.wgsl

@@ -0,0 +1,6 @@
+[[stage(vertex)]]
+fn main([[builtin(vertex_index)]] in_vertex_index: u32) -> [[builtin(position)]] vec4<f32> {
+    let x = f32(1 - i32(in_vertex_index)) * 0.5;
+    let y = f32(1 - i32(in_vertex_index & 1u) * 2) * 0.5;
+    return vec4<f32>(x, y, 0.0, 1.0);
+}