Migrate SKIPIF -> EXTENSIONS (#7138)

This is an automated migration of most SKIPIF extension_loaded checks.

Use standard PDO way for fetching integer attribute values

Make various failure conditions in PDO unconditional errors

This includes TypeErrors, ValueErrors, Error for uninitialized objects
and invalid user classes/callable instanciation

Make various failure conditions in PDO unconditional errors

This includes TypeErrors, ValueErrors, Error for uninitialized objects
and invalid user classes/callable instanciation

Closes GH-6212

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