Fixes#35373.
This changes the example from "run an arbitrary process" to "copy a file". This should make it a bit easier to follow, require less background knowledge to understand, and not use any platform-specific commands that won't work for Windows users.
The most glaring issue with this change is that this doc does not explictly specify how to build and run a builder. I've updated some of the files to hint at this a bit more (such as the `"implementation": "./dist/my-builder.js"`), but another pass is required to figure out the best way to compile a builder and how we want to structure this example to best communicate that.
PR Close#42371
e0381a87c9