Update mlir GDB printers

Update prettyprinters.py to match MLIR changes.

This has gone unnoticed because no build bot is running tests with debug info.

I will look into what we can do about this separately. There is
https://green.lab.llvm.org/green/view/LLDB/job/lldb-cmake/,
from Apple. The Debug Info tests are failing despite the green result.

See https://github.com/llvm/llvm-project/issues/48872.

Note: the llvm-support.gdb test only works with Debug,
but not RelWithDebInfo because some checked symbols are stripped.

Reviewed By: dblaikie

Differential Revision: https://reviews.llvm.org/D116646