Migrate SKIPIF -> EXTENSIONS (#7138)

This is an automated migration of most SKIPIF extension_loaded checks.

Unbork tests for PDO_Firebird

PDO_Firebird raises a warning regarding the unknown SQL syntax, which
we have to silence to avoid run-tests.php to mark the test as borked.

Fix #79106: PDO may fetch wrong column indexes with PDO::FETCH_BOTH

Column names can be numeric strings, so we have to make sure to insert
the column values with the appropriate numeric

Fix #79106: PDO may fetch wrong column indexes with PDO::FETCH_BOTH

Column names can be numeric strings, so we have to make sure to insert
the column values with the appropriate numeric keys, instead of adding
them.

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