Add debug build option to build-wasm-example

[oracle58]

Objective

• Add a --debug flag to build-wasm-example to support debug builds for WebGL2/WebGPU targets.
• Fixes build-wasm-example should have an option for debug builds #18464

Solution

• Added --debug flag to build Wasm examples in debug mode.
• Default remains release mode if --debug is not specified.
• Updated documentation to describe the new flag and usage.

Testing

• Verified debug and release builds for WebGL2 and WebGPU respectively.
• Confirmed wasm artifacts are placed in the correct target dir for each build profile:
  • Debug: target/wasm32-unknown-unknown/debug/examples/
  • Release: target/wasm32-unknown-unknown/release/examples/
• Confirmed wasm-bindgen output is written to: examples/wasm/target/debug , examples/wasm/target/release
• Haven't actually tested running the example

Backend	Profile	Artifacts written	Build success
webgl2	debug	✓	✓
webgl2	release	✓	✓
webpgu	debug	✓	✓
webpgu	release	✓	✓

Examples

Debug

$ cargo run -p build-wasm-example -- --api webgl2 --debug load_gltf

Finished `dev` profile [unoptimized + debuginfo] target(s) in 1m 02s
wasm-bindgen --out-dir examples/wasm/target/debug --out-name wasm_example --target web target/wasm32-unknown-unknown/debug/examples/load_gltf.wasm

Release

$ cargo run -p build-wasm-example -- --api webgl2 load_gltf`

Finished `release` profile [optimized] target(s) in 1m 08s
wasm-bindgen --out-dir examples/wasm/target/release --out-name wasm_example --target web target/wasm32-unknown-unknown/release/examples/load_gltf.wasm

[github-actions]

The generated examples/README.md is out of sync with the example metadata in Cargo.toml or the example readme template. Please run cargo run -p build-templated-pages -- update examples to update it, and commit the file change.