Merge pull request #25271 from fengyuentau:matmul_bias

Merge with https://github.com/opencv/opencv_extra/pull/1158

Todo:

- [x] Fix Attention pattern recognition.
- [x] Handle other backends.

Benchmark:

"VIT_B_32 OCV/CPU", M1, results in milliseconds.

| Model | 4.x | This PR |
| - | - | - |
| VIT_B_32 OCV/CPU | 87.66 | **83.83** |


### Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch
- [x] There is a reference to the original bug report and related work
- [x] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [x] The feature is well documented and sample code can be built with the project CMake

modules/dnn/test/test_graph_simplifier.cpp

@@ -143,4 +143,11 @@ TEST_F(Test_Graph_Simplifier, AttentionSubgraph) {
     test("attention_single_head", "Attention");
 }
 
+TEST_F(Test_Graph_Simplifier, BiasedMatMulSubgraph) {
+    /* Test for 1 subgraphs
+        - BiasedMatMulSubgraph
+    */
+    test("biased_matmul", "MatMul");
+}
+
 }}