Port skipif.inc files to EXTENSIONS

Add CLEAN sections to mysqli and PDO mysql tests

Closes GH-6756.

PDO MySQL: Use native types for results

Previously, PDO MySQL only fetched data as native int/float if
native prepared statements were used. This patch updates PDO to
have the same b

PDO MySQL: Use native types for results

Previously, PDO MySQL only fetched data as native int/float if
native prepared statements were used. This patch updates PDO to
have the same behavior for emulated prepared statements, and thus
removes the largest remaining discrepancy between these two modes.

Note that PDO already has a ATTR_STRINGIFY_FETCHES option to control
whether native types are desired or not. The previous output can
be restored by enabling this option.

Most of the tests make use of that option, because this allows the
tests to work under libmysqlclient as well, which currently always
returns string results (independently of whether native or emulated
PS are used).

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Reindent phpt files

Clean DONE tags from tests

Remove most of the `===DONE===` tags and its variations.
Keep `===DONE===` if the test output otherwise becomes empty.

Closes GH-4872.

Replace dirname(__FILE__) by __DIR__ in tests

Fixed bug #75018, fixed bug #75177

Both are caused by the same cast issue in mysqlnd on 32-bit.