[QNN EP] Support Conv + Clip/Relu fusion (#21537)

### Description
- Supports quantized Conv + Activation on the HTP backend:
- Translates `DQs -> Conv -> Relu/Clip -> Q` into a single QNN Conv
operator if the Relu (or Clip) are redundant.



### Motivation and Context
Expands support for QDQ models created with tools that do not wrap Relu
or Clip with QDQ nodes.

This PR introduces the `IQnnNodeGroup` class. In the same way that a
`NodeUnit` represents a collection of `Nodes`, a `IQnnNodeGroup` can
represent one or more `NodeUnits` that are translated into a QNN
operator. QNN EP parses the ONNX graph to create a list of
`IQnnNodeGroup` objects, each representing a single `NodeUnit` or a
fusion of multiple `NodeUnits`.

onnxruntime/core/framework/node_unit.cc

@@ -4,6 +4,7 @@
 #if !defined(ORT_MINIMAL_BUILD) || defined(ORT_EXTENDED_MINIMAL_BUILD)
 
 #include "node_unit.h"
+#include <utility>
 #include "core/graph/graph_viewer.h"
 
 namespace onnxruntime {
@@ -272,6 +273,20 @@ NodeUnit::NodeUnit(const GraphViewer& graph_viewer, const QDQ::NodeGroup& node_g
   }
 }
 
+NodeUnit::NodeUnit(gsl::span<const Node* const> dq_nodes, const Node& target_node,
+                   gsl::span<const Node* const> q_nodes, Type unit_type,
+                   gsl::span<const NodeUnitIODef> inputs, gsl::span<const NodeUnitIODef> outputs,
+                   size_t input_edge_count, Node::EdgeSet output_edges)
+    : dq_nodes_(dq_nodes.begin(), dq_nodes.end()),
+      target_node_(target_node),
+      q_nodes_(q_nodes.begin(), q_nodes.end()),
+      type_(unit_type),
+      inputs_(inputs.begin(), inputs.end()),
+      outputs_(outputs.begin(), outputs.end()),
+      input_edge_count_(input_edge_count),
+      output_edges_(std::move(output_edges)) {
+}
+
 const std::string& NodeUnit::Domain() const noexcept { return target_node_.Domain(); }
 const std::string& NodeUnit::OpType() const noexcept { return target_node_.OpType(); }
 const std::string& NodeUnit::Name() const noexcept { return target_node_.Name(); }

onnxruntime/core/framework/node_unit.h

@@ -68,6 +68,10 @@ class NodeUnit {
  public:
   explicit NodeUnit(const Node& node);
   explicit NodeUnit(const GraphViewer& graph_viewer, const QDQ::NodeGroup& node_group);
+  NodeUnit(gsl::span<const Node* const> dq_nodes, const Node& target_node,
+           gsl::span<const Node* const> q_nodes, Type unit_type,
+           gsl::span<const NodeUnitIODef> inputs, gsl::span<const NodeUnitIODef> outputs,
+           size_t input_edge_count, Node::EdgeSet output_edges);
 
   Type UnitType() const noexcept { return type_; }