Add a bunch of missing argument types to stubs

Warning to ValueError promotion in Intl extension Part 1

Affects:
- IntlCalendar
- IntlGregorianCalendar
- IntlBreakIterator

Closes GH-5669

Add a few missing parameter types in stubs

Related to GH-5627

Fix IntlGregorianCalendar constructor signature

Give these conversative UNKNOWN defaults and no types, as the
overload is something of a mess.

Fix some UNKNOWN default values

In ext/ffi, ext/intl, ext/mysqli, and ext/pcntl

Generate method entries for ext/intl

Closes GH-5370

Fix the default value of the $length parameter of grapheme_substr()

Do not include the same stub multiple times

Closes GH-5322