Extend QDQPropagation transformer to handle multiple consumers

[adrianlizarraga]

Description

• Extends the QDQPropagationTransformer to propagate DQs (forward) across operators with multiple consumers (previously only supported 1 consumer).
• Adds Slice to the list of operators that the QDQPropagationTransformer can propagate DQ/Q ops across.
• Supports QDQ propagation for opset 21.
• Correctly copies Q or DQ attributes when creating new nodes.

Motivation and Context

The QDQPropagationTransformer fixes up QDQ node units for certain "data movement" ops (e.g., Transpose) by inserting Q -> DQ sequences where necessary. For example, the sequence DQ -> Transpose -> Sigmoid is transformed to DQ -> Transpose -> Q -> DQ -> Sigmoid.

However, this fix-up does not currently support data movement ops with multiple consumers, as in:

DQ -> Transpose --+--> Sigmoid ->
                  |
                  +--> Relu ->
                  |
                  +-> graph_output

With the updates in this PR, the above model can be transformed to:

DQ -> Transpose -> Q --+--> DQ -> Sigmoid ->
                       |
                       +--> DQ -> Relu ->
                       |
                       +--> DQ -> graph_output

This update allows QNN EP to support quantized models created with tools that do not wrap data movement ops in Q/DQ ops.