Use StringBuilder for GetString/GetStringWithArgs, as per upstream

Update dependent code as required

src/fileio_func.h

@@ -26,7 +26,7 @@ void FioRenameFile(const std::string &oldname, const std::string &newname);
 
 const char *FiosGetScreenshotDir();
 
-void SanitizeFilename(char *filename);
+void SanitizeFilename(std::string &filename);
 void AppendPathSeparator(std::string &buf);
 void DeterminePaths(const char *exe, bool only_local_path);
 std::unique_ptr<char[]> ReadFileToMem(const std::string &filename, size_t &lenp, size_t maxsize);