New C++ function name parsing logic

Current implementation of CPlusPlusLanguage::MethodName::Parse() doesn't
get anywhere close to covering full extent of possible function declarations.
It causes incorrect behavior in avoid-stepping and sometimes messes
printing of thread backtrace.

This change implements more methodical parsing logic based on clang
lexer and simple recursive parser.

Examples:
void std::vector<Class, std::allocator<Class>>::_M_emplace_back_aux<Class const&>(Class const&)
void (*&std::_Any_data::_M_access<void (*)()>())()

Differential Revision: https://reviews.llvm.org/D31451

llvm-svn: 299374