[lldb] Add support for demangling D symbols

This is part of https://github.com/dlang/projects/issues/81

 .

This patch enables support for D programming language demangler by using a
pretty printed stacktrace with demangled D symbols, when present.

Signed-off-by: Luís Ferreira <contact@lsferreira.net>

Reviewed By: JDevlieghere, teemperor

Differential Revision: https://reviews.llvm.org/D110578