[lldb] Replace std::isprint/isspace with llvm's locale-independent version

Summary:
LLVM is using its own isPrint/isSpace implementation that doesn't change depending on the current locale. LLDB should do the same
to prevent that internal logic changes depending on the set locale.

Reviewers: JDevlieghere, labath, mib, totally_not_teemperor

Reviewed By: JDevlieghere

Differential Revision: https://reviews.llvm.org/D82175