AAPT2: Fix windows unicode path issues

Mingw64 was being difficult, so instead of defining a wmain entrypoint,
the command line parameters are parsed manually using built-in Windows
methods that support Unicode. The results are converted to UTF8 and
handled just like the rest of the linux/mac version of the code.

This also removes dependencies on std::istream in favour of a
FileInputStream which calls the appropriate unicode version of
open to read a file.

No speed regressions found on Linux or MacOS.

Bug: 62336414
Bug: 63830502
Bug: 65645766
Test: manual
Change-Id: I597da51e33729ed1b98bf246e7e773337fd3fee8
Merged-In: I597da51e33729ed1b98bf246e7e773337fd3fee8
diff --git a/tools/aapt2/io/StringInputStream.h b/tools/aapt2/io/StringInputStream.h
new file mode 100644
index 0000000..ff5b112
--- /dev/null
+++ b/tools/aapt2/io/StringInputStream.h
@@ -0,0 +1,56 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef AAPT_IO_STRINGINPUTSTREAM_H
+#define AAPT_IO_STRINGINPUTSTREAM_H
+
+#include "io/Io.h"
+
+#include "android-base/macros.h"
+#include "androidfw/StringPiece.h"
+
+namespace aapt {
+namespace io {
+
+class StringInputStream : public InputStream {
+ public:
+  explicit StringInputStream(const android::StringPiece& str);
+
+  bool Next(const void** data, size_t* size) override;
+
+  void BackUp(size_t count) override;
+
+  size_t ByteCount() const override;
+
+  inline bool HadError() const override {
+    return false;
+  }
+
+  inline std::string GetError() const override {
+    return {};
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(StringInputStream);
+
+  android::StringPiece str_;
+  size_t offset_;
+};
+
+}  // namespace io
+}  // namespace aapt
+
+#endif  // AAPT_IO_STRINGINPUTSTREAM_H