Fix GH-7939: Cannot unserialize IntlTimeZone objects

As it is now, `IntlTimeZone`, `IntlCalendar` and `IntlDateFormatter`
and some other intl class instances can be serialized, but the

Fix GH-7939: Cannot unserialize IntlTimeZone objects

As it is now, `IntlTimeZone`, `IntlCalendar` and `IntlDateFormatter`
and some other intl class instances can be serialized, but the
representation is meaningless, and unserialization yields uninitialized/
unusable objects. To prevent users from noticing this too late, we deny
serialization of such objects in the first place.

Closes GH-7945.

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Add more specific array return type hints for various extensions - part 2

ext/ftp, ext/gmp, ext/intl

Closes GH-7433

Remove null return type from msgfmt_parse_message()

This doesn't seem to possible. Only false is returned on failure.

Declare tentative return types for ext/intl (#6986)

Generate ext/intl class entries from stubs

Closes GH-6670

Improve parameter names in ext/intl

Closes GH-6309

Generate method entries for ext/intl

Closes GH-5370

Do not include the same stub multiple times

Closes GH-5322

Add stubs for IntlDateFormatter & MessageFormatter

Closes GH-4812