LibDebug: Avoid short lived allocations in DIE::for_each_child

This algorithm is both iterative and recursive, so allocating on every
recursion, or when iterating each child is extremely costly.

Instead allow the on stack DIE to be re-initialized so it can be reused.

Userland/Libraries/LibDebug/Dwarf/DIE.h

@@ -36,6 +36,7 @@ public:
     Optional<u32> parent_offset() const { return m_parent_offset; }
 
 private:
+    void rehydrate_from(u32 offset, Optional<u32> parent_offset);
     CompilationUnit const& m_compilation_unit;
     u32 m_offset { 0 };
     u32 m_data_offset { 0 };