AK: Reduce header dependency graph of String.h

String.h no longer pulls in StringView.h. We do this by moving a bunch
of String functions out-of-line.

Kernel/Devices/KeyboardDevice.cpp

@@ -26,6 +26,7 @@
 
 #include <AK/Assertions.h>
 #include <AK/ByteBuffer.h>
+#include <AK/StringView.h>
 #include <AK/Types.h>
 #include <Kernel/Arch/i386/CPU.h>
 #include <Kernel/Devices/KeyboardDevice.h>

Kernel/Devices/PATAChannel.cpp

@@ -24,9 +24,10 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#include "PATADiskDevice.h"
 #include <AK/ByteBuffer.h>
+#include <AK/StringView.h>
 #include <Kernel/Devices/PATAChannel.h>
+#include <Kernel/Devices/PATADiskDevice.h>
 #include <Kernel/FileSystem/ProcFS.h>
 #include <Kernel/Process.h>
 #include <Kernel/VM/MemoryManager.h>

Kernel/Devices/PATADiskDevice.cpp

@@ -27,6 +27,7 @@
 //#define PATA_DEVICE_DEBUG
 
 #include <AK/Memory.h>
+#include <AK/StringView.h>
 #include <Kernel/Devices/PATAChannel.h>
 #include <Kernel/Devices/PATADiskDevice.h>
 #include <Kernel/FileSystem/FileDescription.h>

Kernel/Devices/SB16.cpp

@@ -25,6 +25,7 @@
  */
 
 #include <AK/Memory.h>
+#include <AK/StringView.h>
 #include <Kernel/Devices/SB16.h>
 #include <Kernel/Thread.h>
 #include <Kernel/VM/AnonymousVMObject.h>