Current implementation of SrcOver was done via multipliers of ColorAttachmentDescriptor (see https://developer.apple.com/documentation/metal/mtlrenderpipelinecolorattachmentdescriptor/1514657-destinationalphablendfactor?language=objc). Need to implement other rules in this way.

NOTE: Some of rules can't be implemented through this multipliers (for example, support of extra-alpha can be done only via shaders). We can implement all rules with shaders and don't use CAD-multipliers. But it's better to implement composite in 2 ways and compare performance.