Get the first index number of a given value for a multi-value attribute. If no value was found 0 is returned.
The parameter "ExactMatch" specifies if exact match will be used for comparing the values. Use '1' or 'T' for exact match and '0' or 'F' for "contains" search. In any case the search is case sensitive.
Example: GetValueIndex('abc,def,ghi', 'de', 'F') returns 0
GetValueIndex('abc,def,ghi', 'de', 'T') returns 2
GetValueIndex('abc,def,ghi', 'DE', 'T') returns 0
GetValueIndex('a,b,c,b','b' ', 'F') returns 2