Android: Use correct encoding when converting strings

The functions with "UTF" in the name use "modified UTF-8" rather
than the standard UTF-8 which Dolphin uses, at least according
to Oracle's documentation, so it is incorrect for us to use them.
This change fixes the problem by converting between UTF-8 and
UTF-16 manually instead of letting JNI do it for us.

Source/Android/jni/AndroidCommon/AndroidCommon.cpp

@@ -5,25 +5,28 @@
 #include "jni/AndroidCommon/AndroidCommon.h"
 
 #include <string>
+#include <string_view>
 #include <vector>
 
 #include <jni.h>
 
+#include "Common/StringUtil.h"
+
 std::string GetJString(JNIEnv* env, jstring jstr)
 {
-  std::string result = "";
-  if (!jstr)
-    return result;
-
-  const char* s = env->GetStringUTFChars(jstr, nullptr);
-  result = s;
-  env->ReleaseStringUTFChars(jstr, s);
-  return result;
+  const jchar* jchars = env->GetStringChars(jstr, nullptr);
+  const jsize length = env->GetStringLength(jstr);
+  const std::u16string_view string_view(reinterpret_cast<const char16_t*>(jchars), length);
+  const std::string converted_string = UTF16ToUTF8(string_view);
+  env->ReleaseStringChars(jstr, jchars);
+  return converted_string;
 }
 
 jstring ToJString(JNIEnv* env, const std::string& str)
 {
-  return env->NewStringUTF(str.c_str());
+  const std::u16string converted_string = UTF8ToUTF16(str);
+  return env->NewString(reinterpret_cast<const jchar*>(converted_string.data()),
+                        converted_string.size());
 }
 
 std::vector<std::string> JStringArrayToVector(JNIEnv* env, jobjectArray array)

Source/Core/Common/StringUtil.cpp

@@ -5,6 +5,7 @@
 #include "Common/StringUtil.h"
 
 #include <algorithm>
+#include <codecvt>
 #include <cstdarg>
 #include <cstddef>
 #include <cstdio>
@@ -33,7 +34,6 @@
 constexpr u32 CODEPAGE_SHIFT_JIS = 932;
 constexpr u32 CODEPAGE_WINDOWS_1252 = 1252;
 #else
-#include <codecvt>
 #include <errno.h>
 #include <iconv.h>
 #include <locale.h>
@@ -590,6 +590,18 @@ std::string UTF16BEToUTF8(const char16_t* str, size_t max_size)
 
 #endif
 
+std::string UTF16ToUTF8(std::u16string_view input)
+{
+  std::wstring_convert<std::codecvt_utf8_utf16<char16_t>, char16_t> converter;
+  return converter.to_bytes(input.data(), input.data() + input.size());
+}
+
+std::u16string UTF8ToUTF16(std::string_view input)
+{
+  std::wstring_convert<std::codecvt_utf8_utf16<char16_t>, char16_t> converter;
+  return converter.from_bytes(input.data(), input.data() + input.size());
+}
+
 #ifdef HAS_STD_FILESYSTEM
 // This is a replacement for path::u8path, which is deprecated starting with C++20.
 std::filesystem::path StringToPath(std::string_view path)

Source/Core/Common/StringUtil.h

@@ -173,6 +173,8 @@ std::string SHIFTJISToUTF8(std::string_view str);
 std::string UTF8ToSHIFTJIS(std::string_view str);
 std::string WStringToUTF8(std::wstring_view str);
 std::string UTF16BEToUTF8(const char16_t* str, size_t max_size);  // Stops at \0
+std::string UTF16ToUTF8(std::u16string_view str);
+std::u16string UTF8ToUTF16(std::string_view str);
 
 #ifdef _WIN32