[DataFormatters] Adjusting libc++ std::list formatter to act better with pointers and references and adding a test to cover a previous related fix
This previous fix https://github.com/llvm-mirror/lldb/commit/5469bda296c183d1b6bf74597c88c9ed667b3145 did not have a test since we did not have a reproducer.
This is related to how formatters deal with pointers and references. The added tests both the new behavior and covers the previous bug fix as well.
Differential Revision: https://reviews.llvm.org/D60588