Generate methods entries from stubs for ext/spl

Closes GH-5458

Store default parameter values of internal functions in arg info

Closes GH-5353. From now on, PHP will have reflection information
about default values of parameters of internal function

Store default parameter values of internal functions in arg info

Closes GH-5353. From now on, PHP will have reflection information
about default values of parameters of internal functions.

Co-authored-by: Nikita Popov <nikita.ppv@gmail.com>

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Merge branch 'PHP-7.4'

* PHP-7.4:
Fix #69264: __debugInfo() ignored while extending SPL classes

Add stubs for SplFileInfo et al.

Closes GH-5287