This probably won't be the final API for getting color spaces
from images, since some formats just store an "is sRGB?" flag
instead of a full profile. Instead, once everything works,
we probably want to give every Bitmap a pointer to some
color space abstraction.
But we can always change this later, once things are further along
and better understood.
When trying to figure out the correct implementation, we now have a very
strong distinction on plugins that are well suited for sniffing, and
plugins that need a MIME type to be chosen.
Instead of having multiple calls to non-static virtual sniff methods for
each Image decoding plugin, we have 2 static methods for each
implementation:
1. The sniff method, which in contrast to the old method, gets a
ReadonlyBytes parameter and ensures we can figure out the result
with zero heap allocations for most implementations.
2. The create method, which just creates a new instance so we don't
expose the constructor to everyone anymore.
In addition to that, we have a new virtual method called initialize,
which has a per-implementation initialization pattern to actually ensure
each implementation can construct a decoder object, and then have a
correct context being applied to it for the actual decoding.
