Automerge: [ComplexDeinterleaving] Use BumpPtrAllocator for CompositeNodes (NFC) (#153217)

I was looking over this pass and noticed it was using shared pointers
for CompositeNodes. However, all nodes are owned by the deinterleaving
graph and are not released until the graph is destroyed. This means a
bump allocator and raw pointers can be used, which have a simpler
ownership model and less overhead than shared pointers.

The changes in this PR are to:
- Add a `SpecificBumpPtrAllocator<CompositeNode>` to the
`ComplexDeinterleavingGraph`
- This allocates new nodes and will deallocate them when the graph is
destroyed
  - Replace `NodePtr` and `RawNodePtr` with  `CompositeNode *`

Author: MacDue