[Inductor][CPP] Enable Epilogue Fusion for Grouped GEMM Template (#143897)

**Summary**
In this PR, we enable the epilogues fusion and code generation for Grouped GEMM. Here are the high-level description of how we implement it.

**Fusion**

- The Grouped GEMM Template produces a `Template Buffer` with a `MultiOutputLayout` and a set of `MultiOutput Buffers`, where each buffer corresponds to a specific GEMM.
- During the initial round of fusion, the `Template Buffer` and all associated `MultiOutput Buffers` are fused into a `FusedSchedulerNode` by extending the existing fusion design.
- In subsequent fusion rounds, this `FusedSchedulerNode` can further fuse with its epilogues, following the original fusion design principles.

**Code Gen**
We maintain a list of epilogues and codegen it one by one.

- If any of the GEMM has bias, we create  a extra `bias_add` epilogue and prepend it at first of the epilogue list.
- If any of the GEMM has no epilogue, we create a `to_bf16` copy epilogue and append it at last of the epilogue list.

**TestPlan**
```
python -u -m pytest -s -v test/inductor/test_cpu_select_algorithm.py -k test_grouped_linear_epilogue
```

Pull Request resolved: https://github.com/pytorch/pytorch/pull/143897
Approved by: https://github.com/jansel, https://github.com/jgong5
ghstack dependencies: #143796

torch/_inductor/utils.py

@@ -1822,6 +1822,31 @@ def pass_execution_and_save(func, gm, inp, msg):
         )
 
 
+def is_multi_outputs_template(input_buf) -> bool:
+    """
+    Check if input buffer is a multi-outputs template buffer
+    """
+    from . import ir
+
+    return isinstance(input_buf, ir.CppTemplateBuffer) and isinstance(
+        input_buf.layout, ir.MultiOutputLayout
+    )
+
+
+def is_output_of_multi_outputs_template(input_buf) -> bool:
+    """
+    Check if input buffer is a output of multi-outputs template buffer
+    """
+    from . import ir
+
+    return (
+        isinstance(input_buf, ir.MultiOutput)
+        and len(input_buf.inputs) == 1
+        and isinstance(input_buf.inputs[0], ir.CppTemplateBuffer)
+        and isinstance(input_buf.inputs[0].layout, ir.MultiOutputLayout)
+    )
+
+
 def is_collective(node, op=None):
     from . import ir