Fixing CAT-1061 issue

Fixing approach : When insert operator in number token divide the number token into another two number token instead of placing the number token by the operator. Example: if current formula is 2* 23, and I want this formula transform into 2 * 2+3 by insert an "+" in 23 the previous version will turn the formula into "2*+" which will  cause the issue cat-1061
You don't use the variable `externFormulaStringBeforeInput ` in your test method. Please remove it. ;)