[lldb] Replace default bodies of special member functions with = default;

Replace default bodies of special member functions with = default;

$ run-clang-tidy.py -header-filter='lldb' -checks='-*,modernize-use-equals-default' -fix ,

https://clang.llvm.org/extra/clang-tidy/checks/modernize-use-equals-default.html

Differential revision: https://reviews.llvm.org/D104041