[js/webgpu] Add activation Tanh (#21540)

Bug:#21467

### Description
<!-- Describe your changes. -->



### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->

js/web/lib/wasm/jsep/webgpu/ops/fuse-utils.ts

@@ -30,6 +30,10 @@ export const getActivationSnippet =
               baseType}(uniforms.beta)));`;
         case 'LeakyRelu':
           return `value = select(${baseType}(uniforms.alpha) * value, value, value >= ${valueType}(0.0));`;
+        case 'Tanh':
+          return `let e2x = exp(-2.0 * abs(value));
+              value = sign(value) * (1.0 - e2x) / (1.0 + e2x);
+        `;
         case '':
           return '';
         // TODO: adding other activations that can be fused.

js/web/test/data/ops/fused-conv.jsonc

@@ -430,5 +430,38 @@
         ]
       }
     ]
+  },
+  {
+    "name": "fused conv with tanh",
+    "operator": "FusedConv",
+    "attributes": [
+      { "name": "activation", "data": "Tanh", "type": "string" },
+      { "name": "kernel_shape", "data": [2, 2], "type": "ints" }
+    ],
+    "opset": { "domain": "com.microsoft", "version": 1 },
+    "cases": [
+      {
+        "name": "T[0]",
+        "inputs": [
+          {
+            "data": [0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9],
+            "dims": [1, 1, 3, 3],
+            "type": "float32"
+          },
+          {
+            "data": [0.11, 0.12, 0.13, 0.14],
+            "dims": [1, 1, 2, 2],
+            "type": "float32"
+          }
+        ],
+        "outputs": [
+          {
+            "data": [0.15572261810302734, 0.20409323275089264, 0.29770541191101074, 0.3425688147544861],
+            "dims": [1, 1, 2, 2],
+            "type": "float32"
+          }
+        ]
+      }
+    ]
   }
 ]