[AllocToken, Clang] Implement TypeHashPointerSplit mode (#156840)

Implement the TypeHashPointerSplit mode: This mode assigns a token ID
based on the hash of the allocated type's name, where the top half
ID-space is reserved for types that contain pointers and the bottom half
for types that do not contain pointers.

This mode with max tokens of 2 (`-falloc-token-max=2`) may also
be valuable for heap hardening strategies that simply separate pointer
types from non-pointer types.

Make it the new default mode.

Link: https://discourse.llvm.org/t/rfc-a-framework-for-allocator-partitioning-hints/87434

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This change is part of the following series:
  1. https://github.com/llvm/llvm-project/pull/160131
  2. https://github.com/llvm/llvm-project/pull/156838
  3. https://github.com/llvm/llvm-project/pull/162098
  4. https://github.com/llvm/llvm-project/pull/162099
  5. https://github.com/llvm/llvm-project/pull/156839
  6. https://github.com/llvm/llvm-project/pull/156840
  7. https://github.com/llvm/llvm-project/pull/156841
  8. https://github.com/llvm/llvm-project/pull/156842

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