mapi: add new _glapi_new_nop_table() and _glapi_set_nop_handler()

mapi: add new _glapi_new_nop_table() and _glapi_set_nop_handler()

_glapi_new_nop_table() creates a new dispatch table populated with
pointers to no-op functions.

_glapi_set_nop_handler() is used to register a callback function which
will be called from each of the no-op functions.

Now we always generate a separate no-op function for each GL entrypoint.
This allows us to do proper stack clean-up for Windows __stdcall and
lets us report the actual function name in error messages.  Before this
change, for non-Windows release builds we used a single no-op function
for all entrypoints.

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>