Reserve "formatter" as a package name

[munificent]

At long last, we're adding support to dart format for configuring page width at the project level. The configuration goes in analysis_options.yaml under a formatter key:

formatter:
  page_width: 123

This is consistent with other top level keys in that file: analyzer and linter. In those latter cases, those keys are also the name of the package. For complicated historical reasons, the formatter's package name is dart_style not formatter. It would probably be confusing if there was a package named formatter that had nothing to do with dart format or the formatter key in analysis_options.yaml.

Is it worth marking that name as reserved? As far as I can tell, there is no package on pub with that name today.

(Long-term, it might be nice to migrate dart_style to that name but that would be a lot of work for marginal benefit.)

[sigurdm]

The "formatter" package name has now been reserved!

[munificent]

Thank you!