Add WASM-specific configurations

I've added a runner override to use the wasm-server-runner for easy
devlopment -- it's a localhost webserver to provide the WASM binary &
it's bootstrap code.

There is also target-specific config related to the RNG back-end.

.cargo/config.toml

@@ -0,0 +1,4 @@
+
+[target.wasm32-unknown-unknown]
+runner = "wasm-server-runner"
+rustflags = ["--cfg", "getrandom_backend=\"wasm_js\""]

Cargo.toml

@@ -10,3 +10,8 @@ rand_chacha = "0.9.0"
 
 [features]
 dynamic_linking = ["bevy/dynamic_linking"]
+
+# For WASM builds, we need to use the browser's RNG back-end.
+# This also requires the extra rustflags in `.cargo/config.toml`
+[target.'cfg(target_arch = "wasm32")'.dependencies]
+getrandom = { version = "0.3.3", features = ["wasm_js"] }