This deprecates all callables that are accepted by
call_user_func($callable) but not by $callable(). In particular:
"self::method"
"parent::method"
"static::method"
["self", "method"]
["parent", "method"]
["static", "method"]
["Foo", "Bar::method"]
[new Foo, "Bar::method"]
RFC: https://wiki.php.net/rfc/deprecate_partially_supported_callables
Closes GH-7446.
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