[Php80] Skip non-zero strpos() offset in StrContainsRector

[guillaume-sainthillier]

str_contains() has no offset, so offset strpos() calls are rewritten with a substr() copy of the haystack (#3086, #5257):

-false === strpos($content, self::TABLE_BORDER, $end + $length)
+!str_contains(substr($content, $end + $length), self::TABLE_BORDER)

This turns an allocation-free search into an O(n) copy on every call, which is what the offset was there to avoid. Real case: silarhi/caf-parser PaymentSlipParser::extractTableContent() walks a large file with offsets, and had to skip the rule (silarhi/caf-parser#111).

1,000 calls on a 1 MB string, offset 1000, PHP 8.5:

case	strpos(..., $offset)	str_contains(substr(...))
needle ~1 KB after offset	0.05 ms	15.4 ms
needle absent	20.1 ms	36.3 ms

Change:

• offset resolving to 0: str_contains($haystack, $needle), no substr()
• any other offset: skipped (also what StrContainsRector incorrectly replaces strpos() when $offset is defined rector#8303 suggested)

[TomasVotruba]

Valid change, thank you 👍