emulator/opengl/emugen: Ensure correct buffer alignment.

The decoders generated by emugen pass addresses that come directly
from the stream to EGL/GL functions. Sometimes, these addresses are
not properly padded with regards to the type of data being transfered
and this can crash some implementations (e.g. OSMesa being compiled
with -msse by default, and doesn't build without it).

This patch introduces two helper classes in ProtocolUtils.h, named
InputBuffer and OutputBuffer, which are used to auto-align buffer
pointers, then make the generated decoder code use them.

Change-Id: I345c7eecc230f62310ced5378b6344f419647e06
Merge "emulator/opengl/emugen: Ensure correct buffer alignment."