Updated AGALMiniAssembler and added AGALMacroAssembler

Obtained from https://github.com/adobe-flash/graphicscorelib

These files are unmodified from Adobe's versions and the updated AGALMiniAssembler works for our existing shaders.
Merging these files independently will make it easier to see the changes I've made in the minimal-shader branch when it's time for a PR there.