webnn: utilize constant nodes in DirectML backend

This CL utilizes `DML_GRAPH_NODE_TYPE_CONSTANT` introduced in
`DML_FEATURE_LEVEL_6_2` for constant scalar inputs, which allows CPU
memory to be directly consumed during graph compilation.

Change-Id: I468e600e0b1dae59a0ab017ef7fe86b5e0e00c59
Bug: 366284850
Cq-Include-Trybots: luci.chromium.try:win11-blink-rel, mac14.arm64-blink-rel, mac14-blink-rel, mac15.arm64-blink-rel, mac15-blink-rel, linux-blink-rel
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5859935
Reviewed-by: Rafael Cintron <rafael.cintron@microsoft.com>
Commit-Queue: Shiyi Zou <shiyi.zou@intel.com>
Reviewed-by: ningxin hu <ningxin.hu@intel.com>
Auto-Submit: Shiyi Zou <shiyi.zou@intel.com>
Cr-Commit-Position: refs/heads/main@{#1367255}

webnn/conformance_tests/subgraph.https.any.js

@@ -2464,6 +2464,65 @@ const subgraphTests = [
       }
     }
   },
+  {
+    'name': 'add + sub + mul + gather default',
+    'graph': {
+      'inputs': {
+        'addA': {
+          'data': [10],
+          'descriptor': {shape: [], dataType: 'int32'},
+          'constant': true
+        },
+        'addB': {
+          'data': [20],
+          'descriptor': {shape: [], dataType: 'int32'},
+          'constant': true
+        },
+        'subB': {
+          'data': [40],
+          'descriptor': {shape: [], dataType: 'int32'},
+        },
+        'divA': {
+          'data': [-20],
+          'descriptor': {shape: [], dataType: 'int32'},
+          'constant': true
+        },
+        'gatherInput': {
+          'data': [0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2],
+          'descriptor': {shape: [3, 4], dataType: 'float32'},
+          'constant': true
+        },
+      },
+      'operators': [
+        {
+          'name': 'add',
+          'arguments': [{'a': 'addA'}, {'b': 'addB'}],
+          'outputs': 'addOutput'
+        },
+        {
+          'name': 'sub',
+          'arguments': [{'a': 'addOutput'}, {'b': 'subB'}],
+          'outputs': 'subOutput'
+        },
+        {
+          'name': 'div',
+          'arguments': [{'a': 'divA'}, {'b': 'subOutput'}],
+          'outputs': 'divOutput'
+        },
+        {
+          'name': 'gather',
+          'arguments': [{'input': 'gatherInput'}, {'indices': 'divOutput'}],
+          'outputs': 'output'
+        },
+      ],
+      'expectedOutputs': {
+        'output': {
+          'data': [0.9, 1.0, 1.1, 1.2],
+          'descriptor': {shape: [4], dataType: 'float32'}
+        }
+      }
+    }
+  },
 ];
 
 if (navigator.ml) {