Refactor "mergeAreaRecords" utility

[kettanaito]

This is a follow up to #208

What:

Need to refactor the src/utils/breakpoints/mergeAreaRecords utility function.

Why:

• It's too smart due to accepting the includesArea flag
• It shouldn't manage the next behavior value
• It should be a simple A + B breakpoints merge, to be used on any two breakpoints in general (now operates on AreaRecord)

[ruhaise]

@kettanaito some more info about this bug would be nice :)

[kettanaito]

Hi, @ruhaise. It's not a bug, but a refactoring of the existing code.

As I said, the function that should merge two area records is too smart. It doesn't have to know if the area is included in the template (represented by includesArea argument), because there is no template at the time of merging. It's used at the moment only to produce the next breakpoint behavior, which I also think should not be this function's concern.

In practice this task means to simplify mergeAreaRecords(), its corresponding unit test, any related integration tests that may use that function, and the usage surface. Since it will no longer accept includesArea, and won't produce next behavior, its call signature will change and would need to be adjusted where it's being used.

Overall, I think it's not a beginner-friendly task, but I don't mean to discorauge you: the library is still quite straightforward, so you will be able to understand the code if you give it a read. Feel free to ping me regarding any questions about this refactoring. Thanks!