[TRTLLM-8160][feat] Add draft token tree runtime on CDL

[yweng0828]

@coderabbitai summary

Description

In this PR, we implemented the runtime logic for the draft token tree. Given the improved performance of capturable drafting loops (CDL), our implementation is also based on CDL. A non-CDL draft PR is available here, but it's not considered for merging: #8109

With this PR, we now have the following features:

1. After the target model completes the prefill phase, the draft model will generate draft tokens based on the static tree.
2. These draft tokens are passed to the target model and forwarded using XQA.
3. Validate which of these draft tokens can be accepted.
4. Generate draft tokens for the first generation step.

Unverified:

1. A new round of validation requires KV cache rewind for the target model (https://github.com/NVIDIA/TensorRT-LLM/pull/8421/files). This will be further tested and updated in a subsequent PR.
2. trtllm-bench test
3. disagg test

Required tests for this PR before merging:
[x] Verify that the current implementation is compatible with CUDA Graph
[x] Verify that this PR does not impact other existing functionality

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