Suggest use as a dev_dependency instead of global install

Why don't we recommend installing webdev as a dev_dependency? ([here](https://pub.dev/packages/webdev#installation)).

Then we could add the constraints
```yaml
dependencies:
build_runner: ^2.4.0
build_web_compilers: ^4.0.4
```
And we would not have to manually validate constraints of the current apps pubspec.lock, but rely on the pub solver to do it..

Maybe I'm missing something obvious. But it seemed to work when I tried.

Review the webdev installation guidance and the current apps' pubspec.yaml and pubspec.lock files. Check whether webdev can be declared as a dev dependency with the proposed build_runner and build_web_compilers constraints, then verify that dependency resolution replaces the current manual validation. Done means the recommendation and project configuration consistently use the pub solver.

Written by the indexing model from the issue text.