REACH-70 Turn GetDefinitionLineIndexMap method into static helper method in CodeBlockUtils.

Also new test cases were written to test this new helper method in various combinations.
It's better to not depend on concrete types, but instead use more abstract types
I would like to use IEnumerable instead of List, but in this class there are a lot of places where used specific implementations.
@Benglin, how do you think, should I keep existing pattern for properties type, or use IEnumerable?