[LLDB] Applying clang-tidy modernize-use-default-member-init over LLDB

Applied modernize-use-default-member-init clang-tidy check over LLDB.
It appears in many files we had already switched to in class member init but
never updated the constructors to reflect that. This check is already present in
the lldb/.clang-tidy config.

Differential Revision: https://reviews.llvm.org/D121481