Move StringPiece to libandroidfw

libandroidfw needs to make use of StringPiece, so
move it to libandroidfw and update all code referencing
StringPiece in aapt2.

Test: make libandroidfw_tests libaapt2_tests
Change-Id: I68d7f0fc7c651b048d9d1f5e7971f10ef5349fa1
diff --git a/tools/aapt2/dump/Dump.cpp b/tools/aapt2/dump/Dump.cpp
index 2920c2a..bcede72 100644
--- a/tools/aapt2/dump/Dump.cpp
+++ b/tools/aapt2/dump/Dump.cpp
@@ -16,6 +16,8 @@
 
 #include <vector>
 
+#include "androidfw/StringPiece.h"
+
 #include "Debug.h"
 #include "Diagnostics.h"
 #include "Flags.h"
@@ -24,7 +26,8 @@
 #include "proto/ProtoSerialize.h"
 #include "unflatten/BinaryResourceParser.h"
 #include "util/Files.h"
-#include "util/StringPiece.h"
+
+using android::StringPiece;
 
 namespace aapt {