Migrate Storybook 6 projects to the Storybook 7 layout

The package-level changes of Storybook 7, without upgrading versions: replaces start-storybook and build-storybook with storybook dev and storybook build (MigrateStorybook7Scripts), moves a renderer plus builder to the framework package and removes the packages Storybook 7 no longer publishes (MigrateStorybook7Packages), moves framework and core.builder of .storybook/main (MigrateStorybook7Config) and adds the storybook package that provides the new CLI. Used by UpgradeToStorybook7 and the later majors, and does nothing to a project that is already past 6.