Add support to PHP 8.3 and drop support of PHP 8.0

[llaville]

With upcoming stable release of PHP 8.3 on November 23rd, 2023, PHP 8.0 will reach End Of Life !

• create branch 8.0
• drop support of PHP 8.0
• new sniffs to detect PHP 8.3 features
  • PHP Core - Readonly Amendments
  • PHP Core - Typed Class Constants -- see commit 25aee3c
  • PHP Core - Closures created from magic methods
  • PHP Core - Override Attribute -- see commit 437403d
  • PHP Core - Static variable initializers -- see commit ddb594e
  • PHP Core - Fetch class constant dynamically syntax -- see commit c23dfb1

[llaville]

Will close this feature report, because major version 8.0 that will drop support to PHP 8.0 will come later in 2024, while in same time, I'll release a Compatinfo version 7.1.0 that will support PHP 8.0, 8.1, 8.2, and 8.3.

FYI /cc @remicollet