Migrate SKIPIF -> EXTENSIONS (#7138)

This is an automated migration of most SKIPIF extension_loaded checks.

Run tidy

This should fix most of the remaining issues with tabs and spaces
being mixed in tests.

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.

Fixed several ext/intl tests

Keep date precision in MessageFormatter.

MessageFormatter::parse and MessageFormat::format (and their static
equivalents) now don't throw away better than second precision in the
arg

Keep date precision in MessageFormatter.

MessageFormatter::parse and MessageFormat::format (and their static
equivalents) now don't throw away better than second precision in the
arguments.

It's already bad enough that in MessageFormatter and IntlDateFormatter we
use seconds since epoch instead of milliseconds since epoch, deviating
from the ICU date representations. But we don't need to throw away extra
precision when parsing dates; we can keep the seconds since epoch
convention and return non integer doubles with only a small BC impact.
Note that we already could return doubles from MessageFormatter::parse if
the date was sufficiently in the past or in the future.

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