[QNN Quantization] Ensure fused nodes have names

[adrianlizarraga]

Description

• Updates the qnn_preprocess_model() method to set a name for any new nodes added to the graph (due to fusion).
• Updates the qnn_preprocess_model() method to set a name for any unnamed nodes that previously existed in the original graph.
• Adds unit tests for fusions (previously missing)
  • Checks that fused node names exist and are unique
  • Checks that fused graph is equivalent to original graph

Motivation and Context

Nodes are not strictly required to have names. However, a planned/upcoming feature to support mixed-precision (integer) quantized models needs nodes to have names.

[jywu-msft]

thanks for adding fusion tests!