[7.x] Statamic 5

[duncanmcclean]

This pull request makes the necessary changes required to support Statamic 5.

This PR will be added to as time goes on.

Changes

• Updates the version constraint in composer.json
• Adjusted testing matrix
• Changed how we call the Antlers parser
  • Previously, we were directly calling the Regex parser. However, the Regex Parser has been removed in Statamic 5 so this updates the code to call Antlers::parser() instead.
• Simplifies the TestCase
  • This was made possible by [5.x] Simplify TestCase for addons statamic/cms#9573.
• Documentation updates
  • Updated install requirements.
  • Added notes about dropped Statamic / Laravel / PHP support.
  • Updated model casts example - casts are now defined in a method.
• Replaces laravel/helpers functions
  • Statamic 5 dropped the laravel/helpers dependency, which provided backwards compatibility for old string/array helpers.
  • We were using some of the helpers provided by this package, so I've replaced them with calls to Laravel's Str class.
• Improved the UX of Runway's commands by introducing Laravel Prompts and using Laravel's console components ($this->components->...)
• The Eloquent Models now use the casts method for defining casts, rather than the $casts property used in older versions of Laravel.

[github-actions]

Released as part of v7.0.0.