[lldb] Fix infinite recursion in Mach-O export trie parsing (#202773)
A malformed (or hostile) export trie whose child offset points back to a
node already on the path from the root (a cycle) made ParseTrieEntries
recurse forever and overflow the stack.
Track the node offsets visited during the walk and reject any trie that
revisits one. Add unit tests for a self-cycle and a back-edge cycle.