Performance improvement for collection cells with many childs (1000+)

In my mps-multiline language (https://github.com/slisson/mps-multiline)  I create a cell for each word. If the text contains 1000+ words and therefore the collection cell of the text has the same amount of childs, the editor performance is bad.

Luckily, it's not a big problem and can be fixed very easily. Here is my proposed solution.