6.0.0: XP 12 compatibility, PHP 7.4+

• Dropped support for XP <= 9, see xp-framework/rfc#341 - @thekid
• Made compatible with XP 12, dropping PHP 7.0 - 7.3 - @thekid
• Added PHP 8.4 to the test matrix - @thekid
• Merged PR #30: Migrate to new reflection API - @thekid