The rendering script service has been extended with APIs to resolve a macro id and to access the macro descriptor:
#set ($macroId = $services.rendering.resolveMacroId('info/xwiki/2.1'))
#set ($macroDescriptor = $services.rendering.getMacroDescriptor($macroId))
#set ($macroDescriptor = $services.rendering.getMacroDescriptor($macroId))
Check the Rendering Module documentation for more information.