Metal backend: Add operator implementations (#15023)

Adds bfloat16/float32 working implementations of the following AOTI shim
ops:
 - aoti_torch_mps_mm_out
 - aoti_torch_mps_convolution
 - aoti_torch_mps__scaled_dot_product_attention_math_for_mps

 Adds a stub implementation of aoti_torch_mps_addmm_out

Author: manuelcandales

backends/apple/metal/runtime/shims/et_metal_ops.h

@@ -0,0 +1,73 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#pragma once
+
+#include <executorch/backends/apple/metal/runtime/shims/types.h>
+
+namespace executorch {
+namespace backends {
+namespace metal {
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * ExecutorTorch implementation of aoti_torch_mps_mm_out.
+ * Performs simple matrix multiplication: out = self @ mat2
+ */
+AOTITorchError aoti_torch_mps_mm_out(
+    AOTITensorHandle out,
+    AOTITensorHandle self,
+    AOTITensorHandle mat2);
+
+/**
+ * ExecutorTorch implementation of aoti_torch_mps_convolution.
+ * Performs 2D convolution operation - matches PyTorch AOTI signature
+ */
+AOTITorchError aoti_torch_mps_convolution(
+    AOTITensorHandle input,
+    AOTITensorHandle weight,
+    AOTITensorHandle* bias,
+    const int64_t* stride,
+    int64_t stride_len_,
+    const int64_t* padding,
+    int64_t padding_len_,
+    const int64_t* dilation,
+    int64_t dilation_len_,
+    int32_t transposed,
+    const int64_t* output_padding,
+    int64_t output_padding_len_,
+    int64_t groups,
+    AOTITensorHandle* ret0);
+
+/**
+ * ExecutorTorch implementation of
+ * aoti_torch_mps__scaled_dot_product_attention_math_for_mps. Performs scaled
+ * dot product attention calculation - matches PyTorch AOTI signature
+ */
+AOTITorchError aoti_torch_mps__scaled_dot_product_attention_math_for_mps(
+    AOTITensorHandle query,
+    AOTITensorHandle key,
+    AOTITensorHandle value,
+    AOTITensorHandle* attn_mask,
+    double dropout_p,
+    int32_t is_causal,
+    AOTITensorHandle* dropout_mask,
+    double* scale,
+    AOTITensorHandle* ret0,
+    AOTITensorHandle* ret1);
+
+#ifdef __cplusplus
+} // extern "C"
+#endif
+
+} // namespace metal
+} // namespace backends
+} // namespace executorch