Update URL of php.net date format table

[iandunn]

There are a lot of /* translators: ... */ comments pointing people to ​https://www.php.net/date to reference the tokens that can be used in date( $format, ... ).

The table has moved from that page, and now lives at ​https://www.php.net/manual/en/datetime.format.php. If a translator doesn't know that already, they'll have to waste time figuring it out. Updating the links would remove that barrier.

[iandunn]

Er, they should probably be changed to https://www.php.net/manual/datetime.format.php instead of https://www.php.net/manual/en/datetime.format.php. I'm guessing php.net automatically redirects it to the user's locale.

[SergeyBiryukov]

In 48991:

Docs: Update the URL for PHP date formats table in translator comments.

Props hareesh-pillai, iandunn.
Fixes #51332.

[SergeyBiryukov]

In 48992:

Twenty Twenty: Update the URL for PHP date formats table in translator comments.

Follow-up to [48991].

Props hareesh-pillai, mukesh27, iandunn.
Fixes #51335. See #51332.