[Flutter Web] Add support for source maps debug id

[buenaflor]

We can inject the debug id into the js file and the sourcemap with sentry-cli and this will be more reliable for symbolication than using releases

sentry-cli sourcemaps inject build/web/main.dart.js build/web/main.dart.js.map
Note: there is currently a bug in the sentry-cli (at least for dart sourcemaps) if you specify the directory and not the individual files it modifies the sourcemap in such a way that it is 'corrupted'. Related issue

The Sentry Flutter package also needs to be updated to be able to read the debug id during runtime