maxColorAttachments property
Two, and settable so a test can be the device that answers one —
gfx-50n.
The reason this is a parameter is that the device it stands in for
cannot be asked. Impeller on OpenGL ES aborts rather than refusing, so
there is no way to run the no-MRT path on the hardware that has it and
see what the engine does. This fake answers what a pass was opened
with; CpuDevice, which takes the same number, answers what came out
the other end as pixels.
Implementation
@override
final int maxColorAttachments;