Enable Msaa for webgl by default (bevyengine#3489)

# Objective

- `Msaa` was disabled in webgl due to a bug in wgpu
- Bug has been fixed (gfx-rs/wgpu#2307) and backported (gfx-rs/wgpu#2327), and updates for [`wgpu-core`](https://crates.io/crates/wgpu-core/0.12.1) and [`wgpu-hal`](https://crates.io/crates/wgpu-hal/0.12.1) have been released

## Solution

- Remove custom config for `Msaa` in webgl
- I also changed two options that were using the arch instead of the `webgl` feature. it shouldn't change much for webgl, but could help if someone wants to target wasm but not webgl2


Co-authored-by: François <[email protected]>

crates/bevy_render/src/options.rs

@@ -13,15 +13,15 @@ pub struct WgpuOptions {
 
 impl Default for WgpuOptions {
     fn default() -> Self {
-        let default_backends = if cfg!(target_arch = "wasm32") {
+        let default_backends = if cfg!(feature = "webgl") {
             Backends::GL
         } else {
             Backends::PRIMARY
         };
 
         let backends = wgpu::util::backend_bits_from_env().unwrap_or(default_backends);
 
-        let limits = if cfg!(target_arch = "wasm32") {
+        let limits = if cfg!(feature = "webgl") {
             wgpu::Limits::downlevel_webgl2_defaults()
         } else {
             #[allow(unused_mut)]

crates/bevy_render/src/view/mod.rs

@@ -49,12 +49,7 @@ pub struct Msaa {
 
 impl Default for Msaa {
     fn default() -> Self {
-        Self {
-            #[cfg(feature = "webgl")]
-            samples: 1,
-            #[cfg(not(feature = "webgl"))]
-            samples: 4,
-        }
+        Self { samples: 4 }
     }
 }