Add gdb/bashdb watchpoints

[rocky]

See http://bashdb.sourceforge.net/bashdb.html#index-watchpoints

and the code https://sourceforge.net/p/bashdb/code/ci/bash-5.1/tree/lib/break.sh and https://sourceforge.net/p/bashdb/code/ci/bash-5.1/tree/command/watch.sh

@roc007 - is this something you'd be interested in?