IR_VERSION

IR VERSION 7 published on <TBD>

• Add support to allow function body graph to rely on multiple external opreator sets.
• Add a list to promote inference graph's initializers to global and mutable variables. Global variables are visible in all graphs of the stored models.
• Add message TrainingInfoProto to store initialization method and training algorithm. The execution of TrainingInfoProto can modify the values of mutable variables.
• Implicitly add inference graph into each TrainingInfoProto's algorithm.