Declare ext/spl constants in stubs (#9226)

Narrow ArrayIterator::key() return type

This can only return string|int|null, not any key type.

Declare tentative return types for ext/spl - part 1 (#7115)

Merge branch 'PHP-8.0'

Various ext/spl stub fixes

Closes GH-7215

Merge branch 'PHP-8.0'

* PHP-8.0:
Fix ArrayObject::exchangeArray() return type

Fix ArrayObject::exchangeArray() return type

This method cannot return null.

Generate ext/spl class entries from stubs

Closes GH-6709

Update ext/spl parameter names

Closes GH-6284.

Add support for `@implementation-alias` in stubs

Closes GH-6170

Add more precise type info for stubs

Closes GH-6005

Fix #79653 Unexpected error for ArrayIterator::ksort()

Closes GH-5644

Generate methods entries from stubs for ext/spl

Closes GH-5458

Merge branch 'PHP-7.4'

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

Add some stubs for SPL

Closes GH-5245