Enhancement : Quantizer only PTQ

Description

Current PTQ relies on a system of tags, and the combination of multiple Meta-Operators to achieve the quantization of a graphView.

While it is functionally working, we argue that it lacks of a general organization, and that the current approach eventually leads to over-complicated code.

In this MR, we propose to only rely on a single meta-operator, the Quantizer, to handle all the graph modifications of the PTQ.

The idea is to initialize the Quantizer to only contain a Mul operator, that performs the scaling operation, and to progressively enrich the meta-operator with the Rounding, Cliping, Cast and BitShift operations.

TODO

• create the new quantizer MetaOperator
• modify the quantizer insertions functions :
• insertProducerScalingNodes()
• insertResidualScalingNodes()
• insertScalingNodes()
• modify the normalization functions :
• normalizeParameters()
• normalizeActivations()
• modify the quantization function
• modify the single-shift related functions
• modify the Cross-Layer Equalization
• modify the Constant-Folding
• modify the "real integer cast" function
• update the unit test