[meta] Add generic methods to call common methods using sai_apis_t st…

…ruct with null ptr check (#1836) (#1837)

Adding 3 sets of apis:

* generic quad apis (create,remove,set,get)
* generic stats apis (get_stats,get_stats_ext,cleart_stats)
* generic quad bulk apis (create,remove,set,get)

all this APIS will have auto generated null pointer check if vendor apis is not implemented.
sai_meta_key_t struct is used as object, for automatic api selection and check.

All this is auto generated from headers.

New method sai_metadata_global_apis_query method is added for easy obtain global apis addresses from given *.so library path. This will be handy in the future when loading libsa.so dynamically.