[WIP][Feature] Implement native fused MoE layer

[yiz-liu]

What this PR does / why we need it?

Enable Expert-Parallel for ascend devices.

Does this PR introduce any user-facing change?

Enable EP
export VLLM_TEST_ENABLE_EP=1

Disable MLA (not supported right now)
export VLLM_MLA_DISABLE=1

How was this patch tested?

git clone https://github.com/yiz-liu/vllm.git
cd vllm
VLLM_TARGET_DEVICE=empty pip install -v -e .

Then install vllm-ascend with this PR.

[wangxiyuan]

see: #127