`Core::System::fstatat()` is similar to our standard `Core::System`
wrappers.
`Core::Directory::stat(relative_path, flags)` is a convenience method if
you already have a Directory, to stat a file relative to it.
`Core::Directory::for_each_entry()` takes a callback which is passed the
DirectoryEntry and the parent Directory. It returns any error from
creating the iterator, iterating the entries, or returned from the
callback.
As a simple example, this:
```c++
Core::DirIterator piece_set_iterator { "/res/icons/chess/sets/",
Core::DirIterator::SkipParentAndBaseDir };
while (piece_set_iterator.has_next())
m_piece_sets.append(piece_set_iterator.next_path());
```
becomes this:
```c++
TRY(Core::Directory::for_each_entry("/res/icons/chess/sets/"sv,
Core::DirIterator::SkipParentAndBaseDir,
[&](auto const& entry, auto&) -> ErrorOr<IterationDecision> {
TRY(m_piece_sets.try_append(entry.name));
return IterationDecision::Continue;
}));
```
`Directory::path()` returning `ErrorOr` makes it awkward to use, and all
current users create a Directory with a path. If we find we need
pathless directories later, we can come up with a clever solution
then. :^)
We have a new, improved string type coming up in AK (OOM aware, no null
state), and while it's going to use UTF-8, the name UTF8String is a
mouthful - so let's free up the String name by renaming the existing
class.
Making the old one have an annoying name will hopefully also help with
quick adoption :^)
Since we already have the directory open, let's have an API to fchown()
the underlying file descriptor instead of forcing clients to do another
path lookup.
These are mostly minor mistakes I've encountered while working on the
removal of StringView(char const*). The usage of builder.put_string over
Format<FormatString>::format is preferrable as it will avoid the
indirection altogether when there's no formatting to be done. Similarly,
there is no need to do format(builder, "{}", number) when
builder.put_u64(number) works equally well.
Additionally a few Strings where only constant strings were used are
replaced with StringViews.
Core::Directory represents an existing directory on the system, and it
holds an actual file descriptor so that the user can be sure the
directory stays in existence.
