webgl feature renamed to webgl2 (#9370)

Addresses:
```sh
$ cargo build --release --example lighting --target wasm32-unknown-unknown --features webgl
error: none of the selected packages contains these features: webgl, did you mean: webgl2, webp?
```

# Objective

- When following the instructions for the web examples.
- Document clearly the generated file `./target/wasm_example.js`, since
it didn't appear on `git grep` (missing extension)

## Solution

- Follow the feature rename on the docs.

---------

Signed-off-by: Seb Ospina <[email protected]>

docs-template/EXAMPLE_README.md.tpl

@@ -210,15 +210,15 @@ Following is an example for `lighting`. For other examples, change the `lighting
 following commands.
 
 ```sh
-cargo build --release --example lighting --target wasm32-unknown-unknown --features webgl
+cargo build --release --example lighting --target wasm32-unknown-unknown
 wasm-bindgen --out-name wasm_example \
   --out-dir examples/wasm/target \
   --target web target/wasm32-unknown-unknown/release/examples/lighting.wasm
 ```
 
 The first command will build the example for the wasm target, creating a binary. Then,
 [wasm-bindgen-cli](https://rustwasm.github.io/wasm-bindgen/reference/cli.html) is used to create
-javascript bindings to this wasm file, which can be loaded using this
+javascript bindings to this wasm file in the output file `examples/wasm/target/wasm_example.js`, which can be loaded using this
 [example HTML file](./wasm/index.html).
 
 Then serve `examples/wasm` directory to browser. i.e.

examples/README.md

@@ -507,15 +507,15 @@ Following is an example for `lighting`. For other examples, change the `lighting
 following commands.
 
 ```sh
-cargo build --release --example lighting --target wasm32-unknown-unknown --features webgl
+cargo build --release --example lighting --target wasm32-unknown-unknown
 wasm-bindgen --out-name wasm_example \
   --out-dir examples/wasm/target \
   --target web target/wasm32-unknown-unknown/release/examples/lighting.wasm
 ```
 
 The first command will build the example for the wasm target, creating a binary. Then,
 [wasm-bindgen-cli](https://rustwasm.github.io/wasm-bindgen/reference/cli.html) is used to create
-javascript bindings to this wasm file, which can be loaded using this
+javascript bindings to this wasm file in the output file `examples/wasm/target/wasm_example.js`, which can be loaded using this
 [example HTML file](./wasm/index.html).
 
 Then serve `examples/wasm` directory to browser. i.e.