Translator changes and class cache (Breaking-L)

Included in this release:

• Translators: Added actual syntax classes that extend BaseSyntax.
• Translators: Added SyntaxInterface.
• Translators: Syntaxes are now loaded using the class cache.
• Translators: Added the SYNTAX_NAME constant to the syntax classes.
• Translators: Narrowed the type of the createApacheVelocity() method.
• Translators: Narrowed the type of the createHubL() method.
• Translators: Added the Mailcode_Translator::create() factory method.
• ShowPhone: Updated some example phone numbers from PhoneLib.
• Core: Added Mailcode::setCacheFolder() to set the cache folder.
• Core: Added the ClassCache class to handle dynamic class loading and caching.
• Code: Minor code tweaks for PHPStan recommendations.
• Code: PHPStan clean @ level 9.

Breaking changes

• It is now mandatory to set a cache folder with Mailcode::setCacheFolder().
• The Apache velocity and HubL translator syntax classes have been renamed.