Clarify forward_static_call docs

[zonuexe]

This PR replaces #5681 and has been rebased on the latest master after 846dfb8.

Commit 846dfb8 clarified that forward_static_call_array() does not require an active class scope and behaves like call_user_func_array() when called outside a class context.

This PR keeps that correction and focuses on the remaining parts not covered by that commit:

• clarifying that forward_static_call() is not limited to calling static methods, but preserves the current called class for method callbacks
• explaining how this relates to late static binding, where static:: resolves to the current called class
• clarifying that this is useful for static method callbacks that should behave like forwarding calls such as parent:: or self::
• updating the forward_static_call_array() parameter note to match call_user_func_array(): parameters can be passed by reference when the corresponding element in the args array is a reference