ext/pdo: document the PHP 8.5 fetch mode changes and deprecations

[lacatoire]

Documents the PHP 8.5 fetch mode changes and deprecations of ext/pdo: the new constant values, the ValueErrors thrown for PDO::FETCH_INTO and PDO::FETCH_PROPS_LATE, the CUFA semantics of the PDO::FETCH_CLASS constructor arguments, the Error thrown when PDOStatement::setFetchMode() is called during a fetch, the deprecation of the uri: DSN scheme and of the driver specific constants and methods, and the Firebird cursor name ValueError.

Tracker items:

• [PDO] setFetchMode during a fetch: PHP 8.5 Documentation Tracker (view)
• [PDO] FETCH_PROPS_LATE ValueError: PHP 8.5 Documentation Tracker (view)
• [PDO] FETCH_INTO ValueError: PHP 8.5 Documentation Tracker (view)
• [PDO] FETCH_CLASS constructor arguments: PHP 8.5 Documentation Tracker (view)
• [PDO] fetch constant values changed: PHP 8.5 Documentation Tracker (view)
• [PDO] uri: DSN scheme deprecated: PHP 8.5 Documentation Tracker (view)
• [PDO] driver specific constants deprecated: PHP 8.5 Documentation Tracker (view)
• [PDO] driver specific methods deprecated: PHP 8.5 Documentation Tracker (view)
• [PDO_FIREBIRD] cursor name ValueError: PHP 8.5 Documentation Tracker (view)