Add runtime detection for PHP 8.6+ SplFileObject iterator fix (php/php-src#21679)

[rene-hermenau]

Problem

PHP PR php/php-src#21679 (merged into php-src master = PHP 8.6) fixes 5 SplFileObject iterator desync bugs (GH-8561 through GH-8564, GH-8851) that existed since PHP 8.0.1. Our AbstractFileObject class has version-specific workarounds for these bugs. When the fix ships, the workarounds will actively break things.

Solution

Add a runtime behavior probe that detects whether the current PHP has the fix, instead of version checks (the fix could be backported to any patch release). When fixed PHP is detected, all methods delegate to parent SplFileObject. Existing workarounds for PHP 7.0-8.5 stay untouched.

References

• PHP PR: Fix GH-8561, GH-8562, GH-8563, GH-8564: SplFileObject iterator desync php/php-src#21679
• PHP issue: Feedback: Please let us know if #21679 fixes in SplFileObject will be backported or not php/php-src#21742
• Pro repo issue: wp-staging/wp-staging-pro#5081