mesa: Generate a helper function for each extension

mesa: Generate a helper function for each extension

Generate functions which determine if an extension is supported in the
current context. Initially, enums were going to be explicitly used with
_mesa_extension_supported(). The idea to embed the function and enums
into generated helper functions was suggested by Kristian Høgsberg.

For performance, the function body no longer uses
_mesa_extension_supported() and, as suggested by Chad Versace, the
functions are also declared static inline.

v2: Place function qualifiers on separate line (Chad)
v3: Move function curly brace to new line (Chad)

Signed-off-by: Nanley Chery <nanley.g.chery@intel.com>
Reviewed-by: Chad Versace <chad.versace@intel.com>