LibCore+Everywhere: Make Core::Stream::read() return Bytes

A mistake I've repeatedly made is along these lines:
```c++
auto nread = TRY(source_file->read(buffer));
TRY(destination_file->write(buffer));
```

It's a little clunky to have to create a Bytes or StringView from the
buffer's data pointer and the nread, and easy to forget and just use
the buffer. So, this patch changes the read() function to return a
Bytes of the data that were just read.

The other read_foo() methods will be modified in the same way in
subsequent commits.

Fixes #13687

Userland/Libraries/LibHTTP/Job.cpp

@@ -172,7 +172,7 @@ ErrorOr<ByteBuffer> Job::receive(size_t size)
         auto result = m_socket->read(buffer);
         if (result.is_error() && result.error().is_errno() && result.error().code() == EINTR)
             continue;
-        nread = TRY(result);
+        nread = TRY(result).size();
         break;
     } while (true);
     return buffer.slice(0, nread);