IOS HLE: More robust escaping of NAND paths

Prevents path traversal without needing an absolute path
function, and also improves accuracy (character sequences
like ../ appear to have no special meaning in IOS).

This removes the creation and usage of /sys/replace,
because the new escapes are too complicated to all
be representable in its format and because no other
NAND handling software seems to use /sys/replace.

Source/Core/Common/StringUtil.cpp

@@ -10,7 +10,9 @@
 #include <cstring>
 #include <iomanip>
 #include <istream>
+#include <iterator>
 #include <limits.h>
+#include <sstream>
 #include <string>
 #include <vector>
 
@@ -328,6 +330,21 @@ void SplitString(const std::string& str, const char delim, std::vector<std::stri
   output.pop_back();
 }
 
+std::string JoinStrings(const std::vector<std::string>& strings, const std::string& delimiter)
+{
+  // Check if we can return early, just for speed
+  if (strings.empty())
+    return "";
+
+  std::stringstream res;
+  std::copy(strings.begin(), strings.end(),
+            std::ostream_iterator<std::string>(res, delimiter.c_str()));
+
+  // Drop the trailing delimiter.
+  std::string joined = res.str();
+  return joined.substr(0, joined.length() - delimiter.length());
+}
+
 std::string TabsToSpaces(int tab_size, const std::string& in)
 {
   const std::string spaces(tab_size, ' ');