[Triton] Centralize Ascend extension op dispatch in triton_utils (#6937)

### What this PR does / why we need it?

This pull request refactors the dispatch mechanism for the
**triton-ascend-specific operators** `insert_slice`, `extract_slice`,
and `get_element` to ensure compatibility with both CANN 8.5 and 9.0.

A unified helper function, `_resolve_triton_ascend_op`, has been
introduced in `vllm_ascend/ops/triton/triton_utils.py`. This function
dynamically resolves these operators by first attempting to import them
from the `triton.language.extra.cann.extension` module, which is present
in newer CANN versions. If that fails, it falls back to the standard
`triton.language` module.

This approach centralizes operator dispatch logic, allowing individual
Triton kernels to use these functions without being aware of the
underlying Triton/CANN version. All call sites have been updated to use
these new unified functions.

### Does this PR introduce _any_ user-facing change?

No. This is an internal refactoring of operator implementations and does
not introduce any user-facing changes.

### How was this patch tested?

CI is expected to pass with existing tests.

**Testing Context:**
- vLLM version: v0.16.0
- vLLM main: `15d76f74e2fdb12a95ea00f0ca283acf6219a2b7`

Signed-off-by: linfeng-yuan <1102311262@qq.com>

vllm_ascend/ops/triton/triton_utils.py

@@ -1,10 +1,46 @@
 from typing import Any
 
 import torch
-from vllm.triton_utils import HAS_TRITON, triton
+from vllm.triton_utils import HAS_TRITON, tl, triton
 
 _NUM_AICORE = -1
 _NUM_VECTORCORE = -1
+_extension_module = None
+
+if HAS_TRITON:
+    try:
+        import triton.language.extra.cann.extension as _extension_module  # type: ignore
+    except ImportError:
+        _extension_module = None
+
+
+def _resolve_triton_ascend_op(op_name: str):
+    if not HAS_TRITON:
+        raise RuntimeError(f"Triton op '{op_name}' cannot be resolved because HAS_TRITON is False")
+
+    if _extension_module is not None:
+        extension_op = getattr(_extension_module, op_name, None)
+        if extension_op is not None:
+            return extension_op
+
+    tl_op = getattr(tl, op_name, None)
+    if tl_op is not None:
+        return tl_op
+
+    raise RuntimeError(
+        f"Failed to resolve Triton op '{op_name}': "
+        "neither triton.language.extra.cann.extension nor triton.language provides it."
+    )
+
+
+if HAS_TRITON:
+    insert_slice = _resolve_triton_ascend_op("insert_slice")
+    extract_slice = _resolve_triton_ascend_op("extract_slice")
+    get_element = _resolve_triton_ascend_op("get_element")
+else:
+    insert_slice = None
+    extract_slice = None
+    get_element = None
 
 
 def init_device_properties_triton():