Debug documentation issues

### Describe the bug

The debug instructions will not work as written, because the `briefcase build` and `briefcase run` commands don't include `-r`. So if pip has already been run, which happens during `briefcase create` on most if not all platforms, it won't be rerun, and the app will be built without the debug components. The app will still start, but it won't wait for the debugger to connect. When you hit the first breakpoint, it will print the current line of code and then immediately crash with a `BdbQuit` exception.

I guess `--debug` mode should work the same as `--test` mode in this respect, but I'm not familiar enough with the code to know whether this is a documentation-only issue, or whether something could be improved in the implementation short of full-blown dependency tracking (#807).

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@freakboy3742: I don't know if this was mentioned somewhere in the gigantic discussion of #2173, but at what point are we going to stop calling this "experimental"? The design seems quite complete, even if it isn't implemented on every platform, so I'm not sure why we're calling it out in this way.

Once we remove those paragraphs from the `build` and `dev` pages, the `pdb` and `vscode` pages can become the single source of truth about which platforms they support.

### Environment

- Software versions:
- Briefcase: 0.3.27

Start with the debug instructions covering `briefcase build` and `briefcase run`, and compare their behavior with `--test` mode. Review the `build` and `dev` pages plus the `pdb` and `vscode` pages; done means the commands work as documented and the platform-support guidance has one clear source of truth.

Written by the indexing model from the issue text.