Userland: Use CFile inside sysctl

Also add a StringView overload to CIODevice::write

LibCore/CIODevice.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <AK/ByteBuffer.h>
+#include <AK/StringView.h>
 #include <LibCore/CObject.h>
 
 class CIODevice : public CObject {
@@ -32,6 +33,7 @@ public:
     ByteBuffer read_all();
 
     bool write(const byte*, int size);
+    bool write(const AK::StringView& v) { return write((const byte*)v.characters(), v.length()); }
 
     // FIXME: I would like this to be const but currently it needs to call populate_read_buffer().
     bool can_read_line();