Convert iterable into an internal alias for Traversable|array (#7309)

This does a compile time transformation of ``iterable`` into ``Traversable|array`` which simplifies some of the LSP vari

Convert iterable into an internal alias for Traversable|array (#7309)

This does a compile time transformation of ``iterable`` into ``Traversable|array`` which simplifies some of the LSP variance handling.

The arginfo generation script from stubs is updated to produce a union type when it encounters the type ``iterable``
Extension functions which do not regenerate the arginfo, or write them manually are still supported by mimicking the compile time transformation while registering the function.

Type Reflection is preserved for single ``iterable`` (and ``?iterable``) to produce a ReflectionNamedType with name ``iterable``, however usage of ``iterable`` in union types will be converted to ``array|Traversable``

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Fix weakmap API test

Apparently under some targets the address can evaluate to an address with the most significant bit set. (displays as negative number)

Add ZEND_API for weakmap functionality via zend_weakrefs_hash_add/del

Closes GH-7600.