improve testing of the 'dart fix' data

[devoncarew]

• improve testing of the 'dart fix' data
• remove fix data references to previous package:web types we no longer generate

When we reduced the number of generated APIs we stopped generating some classes referenced in the lib/fix_data.yaml file. Our testing didn't catch this, since the running dart fix --compare-to-golden just mechanically confirms that it can transform the file, not whether the resulting file is error free.

This PR creates a new temporary project with the test_fixes/renames.dart file - which contains the older dart:html type names - runs dart fix on that project, to update the references to the new package:web names, and runs dart analyze to make sure the result has no analysis issues.

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[kevmoo]

I like this lint. How'd you hit it?

[devoncarew]

In the test_fixes/renames.dart file (which to be honest isn't really intended to be best practice dart code). From memory, I've also hit it a few other times where it was false positives.