[FEA]: Debugger pretty-printers: `cuda::hierarchy`

[Jacobfaib]

Create a lldb and gdb pretty printer for cuda::hierarchy.

The printer should live under libcudacxx/share/libcudacxx/<debugger>/hierarchy.py for each debugger.

In addition, the pretty printers should be exhaustively tested, with tests living under libcudacxx/test/debugging/hierarchy. See the existing tests in that directory for inspiration.