[lldb] Add -m option to 'target modules dump symtab' to disable demangling

Summary: This option was added downstream in swift-lldb. This upstreams this option as it seems useful and also adds the missing tests.

Reviewers: #lldb, kwk, labath

Reviewed By: kwk, labath

Subscribers: labath, kwk, abidh, JDevlieghere, lldb-commits

Tags: #lldb, #upstreaming_lldb_s_downstream_patches

Differential Revision: https://reviews.llvm.org/D69944