Translate:

document.S.Length == n 

to:

{ S : /^.{n}$/s } 

in filters. Also support other comparisons (<, <=, !=, >=, >).

Translate `document.S.Count() == n` in the same way as `Length`.

As usual, support ToLower, ToUpper, Trim, TrimEnd and TrimStart between `document.S` and `Length`