[Perf]enable prefill flashcommon3 (#4065)

### What this PR does / why we need it?
moe multistream overlap to improve the performance.

### How was this patch tested?
--additional-config '{"multistream_overlap_gate": true}'

- vLLM version: v0.12.0
- vLLM main:
ad32e3e19c

---------

Signed-off-by: AlvisGong <gwly0401@163.com>
Signed-off-by: chenxiao <Jaychou1620@Gmail.com>
Co-authored-by: clrs97 <524936896@qq.com>
Co-authored-by: zzhx1 <zzh_201018@outlook.com>
Co-authored-by: chenxiao <Jaychou1620@Gmail.com>

vllm_ascend/flash_common3_context.py

@@ -0,0 +1,42 @@
+from dataclasses import dataclass
+from typing import Optional
+
+import torch
+from vllm.model_executor.layers.linear import LinearBase
+
+
+@dataclass
+class FlashCommon3Context:
+    gate: Optional[LinearBase] = None
+    topk_weights: Optional[torch.Tensor] = None
+    topk_ids: Optional[torch.Tensor] = None
+    row_idx: Optional[torch.Tensor] = None
+    shared_experts: Optional[torch.nn.Module] = None
+    shared_out: Optional[torch.Tensor] = None
+
+
+_flash_common3_context: Optional[FlashCommon3Context] = None
+
+
+def get_flash_common3_context() -> Optional[FlashCommon3Context]:
+    return _flash_common3_context
+
+
+def set_flash_common3_context(
+    topk_weights: Optional[torch.Tensor] = None,
+    topk_ids: Optional[torch.Tensor] = None,
+    shared_experts: Optional[torch.nn.Module] = None,
+    shared_out: Optional[torch.Tensor] = None,
+):
+    global _flash_common3_context
+    if _flash_common3_context is None:
+        _flash_common3_context = FlashCommon3Context()
+
+    if topk_weights is not None:
+        _flash_common3_context.topk_weights = topk_weights
+    if topk_ids is not None:
+        _flash_common3_context.topk_ids = topk_ids
+    if shared_experts is not None:
+        _flash_common3_context.shared_experts = shared_experts
+    if shared_out is not None:
+        _flash_common3_context.shared_out = shared_out