This patch allows an auto-generated GLES encoder function to write
'isLarge' buffers with a custom writer, instead of calling stream->readFully()
directly.
This is intended to allow writing pixel or vertex data that is stored
with a specific stride.
Another patch will introduce the corresponding changes to the .attrib files
Change-Id: I6ca86b968cd3f4db91676bc485ee1e84419e50e0