[#1684] Rewrite statements recognition mechanism

Problem: the current statements recognition mechanism doesn't
comply with statement locations recording mechanism.
An example:
```ocaml
let sum = List.fold (fun (acc, cur) -> acc + cur) [1; 2; 3] 0
```
If we'll go inside aux function then statement locations cache would
be cleaned up and we'll record some redundant locations
(like `let sum = ...`).

Solution: restrict the range of statements searching. For more information
read comments in `getStatements` function in `Snapshots` module.