[libc++] Heap operations on `std::deque` regressed between LLVM 20 and LLVM 22

A is LLVM 20, B is LLVM 22

The issue provides only an image comparing LLVM 20 (A) with LLVM 22 (B), with no source file, test, or reproducer named. Begin by obtaining the comparison details from the attached image and reproducing the heap-operation behavior on std::deque with both LLVM versions. Done means the regression is isolated and the corrected behavior is covered by an appropriate regression test.

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