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

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

从入口点 FFI::cdef()、zend_ffi_handlers.get_method 以及关联 issue #8585 中的讨论开始。确定返回 FFI\CDef 并将其传递给非 static 方法的兼容性影响；完成的要求是达成一致的 API 设计，而不是留下未解决的提案。