Chage FFI::cdef() return FFI\CDef object

[chopins]

Description

Now, FFI::cdef() return a FFI object, then through FFI object call C function.
The above reasons cause some method support call by statically and non-statically, and these method will need exclude in zend_ffi_handlers.get_method. if C DLL has same name function will not be call, or add new FFI method must insert to execlude list.
So suggest FFI::cdef() return object of other class, For example use FFI\CDef instead of FFI object.
FFI\CDef is not construrct and extend in PHP code, Similarly FFI\CData.
Through FFI\CDef of zend_ffi_handlers.get_method will call C function. and FFI non-statically method add one paramter receive FFI\CDef object. this is cause in compatibility.

see: #8585