IOFormatSaver

[WeiqunZhang]

Add a class that can be used to save and restore IO stream format in a RAII way. Below is an example.

auto& os = amrex::OutStream();
auto old_fill = os.fill();
auto old_flags = os.flags();
auto old_precision = os.precision();
auto old_width = os.width();

{
    IOFormatSaver iofmtsaver(os);

    os << std::setfill('x');
    os << std::left;
    os << std::setprecision(4);
    os << std::setw(111);
}

AMREX_ALWAYS_ASSERT(old_fill == os.fill());
AMREX_ALWAYS_ASSERT(old_flags == os.flags());
AMREX_ALWAYS_ASSERT(old_precision == os.precision());
AMREX_ALWAYS_ASSERT(old_width == os.width());