[Feature] support aclgraph for model runner v2 (#7110)

### What this PR does / why we need it?
This PR aims to support aclgraph for model runner v2, please see RFC
#5208. The PR contains these modifications:
- adapt to newest commit of vllm main branch.
- supply a unified interface of extra forward context for both model
runner v1 and model runner v2.
- implement graph mode for main model. 

### Does this PR introduce _any_ user-facing change?
no

### How was this patch tested?

- vLLM version: v0.16.0
- vLLM main:
4034c3d32e

---------

Signed-off-by: Ronald1995 <ronaldautomobile@163.com>

vllm_ascend/distributed/utils.py

@@ -3,6 +3,7 @@ import torch.distributed as dist
 from vllm.distributed.parallel_state import GroupCoordinator, get_dp_group
 from vllm.forward_context import get_forward_context
 
+from vllm_ascend.ascend_forward_context import _EXTRA_CTX
 from vllm_ascend.distributed.parallel_state import get_fc3_quant_x_group
 
 
@@ -16,7 +17,7 @@ def fc3_all_gather_and_maybe_unpad_impl(
     x = get_fc3_quant_x_group().all_gather(x, 0)
     dp_metadata = forward_context.dp_metadata
     if dp_metadata is None:
-        pad_size = forward_context.pad_size
+        pad_size = _EXTRA_CTX.pad_size
         if pad_size > 0:
             x = x[:-pad_size]
     else:
@@ -24,7 +25,7 @@ def fc3_all_gather_and_maybe_unpad_impl(
         num_tokens_across_dp_cpu = dp_metadata.num_tokens_across_dp_cpu
         result = torch.empty((num_tokens_across_dp_cpu.sum(), *x.shape[1:]), device=x.device, dtype=x.dtype)
         dp_size = get_dp_group().world_size
-        x = x.view(dp_size, forward_context.padded_length, *x.shape[1:])
+        x = x.view(dp_size, _EXTRA_CTX.padded_length, *x.shape[1:])
         offset = 0
         for idx in range(dp_size):
             num_tokens_dp = num_tokens_across_dp_cpu[idx]