System.Data.SQLite

.NET Standard 2.1 introduced the method `Marshal.PtrToStringUTF8`, which can be used in `SQLiteConvert.UTF8ToString` (similar to using `Marshal.PtrToStringUni` in `SQLite3_UTF16.UTF16ToString`), in order to save allocation of a byte array and to avoid `Marshal.ReadByte()` when using the standard SQLite library.

For example:

```c#
    public static string UTF8ToString(IntPtr nativestring, int nativestringlen)
    {
      if (nativestring == IntPtr.Zero || nativestringlen == 0) return String.Empty;

#if NETSTANDARD && !NETSTANDARD2_0
      if (nativestringlen < 0)
        return Marshal.PtrToStringUTF8(nativestring);
      else
        return Marshal.PtrToStringUTF8(nativestring, nativestringlen);
#else
      if (nativestringlen < 0)
      {
        nativestringlen = 0;

        while (Marshal.ReadByte(nativestring, nativestringlen) != 0)
          nativestringlen++;

        if (nativestringlen == 0) return String.Empty;
      }

      byte[] byteArray = new byte[nativestringlen];

      Marshal.Copy(nativestring, byteArray, 0, nativestringlen);

      return _utf8.GetString(byteArray, 0, nativestringlen);
#endif
        }
```

Thank you!

Fixed on trunk via check-in [9f4378b8510f62b5].