New mapper (MOS-1827)

[kniazkov]

Cool Story:
The differential tree isn't being constructed optimally when there are many changes, especially in cases where multiple methods are added or removed from a class (all changes occur within a single node representing the class body), or when multiple lines are added, modified, or removed within a method (changes are contained within a single node representing the method body). The greedy algorithm used in this scenario attempts to match the first child nodes, but this is not the most efficient approach. As a result, the differential tree ends up being "crooked," which leads to similarly flawed patterns being generated.

Task:
Refactor the differential tree construction algorithm to handle complex changes more efficiently, particularly when multiple modifications occur within a single node (such as class bodies or method bodies). Improve the tree-building logic so that it avoids suboptimal matches and ensures that the resulting patterns are accurate.

[kniazkov]

@rultor merge

[rultor]

@rultor merge

@kniazkov OK, I'll try to merge now. You can check the progress of the merge here.

[rultor]

@rultor merge

@kniazkov Done! FYI, the full log is here (took me 8min).