[5.x] Update our custom string based rules to class based rules

[jesseleite]

Validation rule changes

As an extension to #9778 and #9780, this PR refactors our old custom validation rule classes in the Statamic\Validation namespace, to proper Laravel ValidationRule implementations within Statamic\Rules, and also removes string based

Validation builder changes

As for the custom rules we had defined in our old ValidationServiceProvider, we now explicitly define which custom rules get added to the validation builder in our Rules.js object:

It makes sense for people to add extra unique validation rules in their own blueprints, but we don't think it ever made sense for unique_form_handle or code_fieldtype_rulers to appear in the builder UI, so these will no longer show 👌

Todo

• Update ClassRuleParser and Fields\Validator to properly handle
  • {collection} style replacements
  • null values
  • true / false booleans
• Move and update
  • UniqueEntryValue rule
    • Should also be accessible to users in validation builder UI
  • UniqueTermValue rule
    • Should also be accessible to users in validation builder UI
  • UniqueUserValue rule
    • Should also be accessible to users in validation builder UI
  • UniqueFormHandle rule
  • CodeFieldtypeRulers rule
• Remove string based rule implementations (breaking)
  • Update script
    • Add test coverage
      • Note: Because string replacements on blueprints/fieldsets could get hairy, I made the script only attempt to replace strict single-quote surrounded rule usages. For example, if the user copied out of the docs, or saved the blueprint from the CP, they'll have single quotes around their rules. By making these replacements strict, the regex should never overzealously replace too much. If they're using these rules in a pipe-delimited rule string for some reason, we can mention that they'll need to use the new class-based rules in the upgrade guide.
• Update tests
• Update docs
  • [5.x] Update string based validation rules docs#1298