[lldb/Command] Add --force option for `watchpoint delete` command

Currently, there is no option to delete all the watchpoint without LLDB
asking for a confirmation. Besides making the watchpoint delete command
homogeneous with the breakpoint delete command, this option could also
become handy to trigger automated watchpoint deletion i.e. using
breakpoint actions.

rdar://42560586

Differential Revision: https://reviews.llvm.org/D72096



Signed-off-by: Med Ismail Bennani <medismail.bennani@gmail.com>