### What this PR does / why we need it?
we implement set_additional_forward_context in platform, it's necessary
to reuse code of gpu in model runner v2 by inheriting method in gpu
model runer v2. please see model runner v2's plan #5208
### Does this PR introduce _any_ user-facing change?
no
### How was this patch tested?
- vLLM version: v0.13.0
- vLLM main:
2f4e6548ef
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Signed-off-by: Ronald1995 <ronaldautomobile@163.com>