fix(interactive): consider path direction in path concat

[BingqingLyu]

What do these changes do?

As titled.
Now we specify the concat position in PathConcat. e.g., Assuming we want to concat left path L with right path R, then we would specify the concat position as follows:

1. concat L=[1,2,3] and R=[3,4,5] with L.end and R.start,
2. concat L=[1,2,3] and R=[5,4,3] with L.end and R.end,
3. concat L=[3,2,1] and R=[3,4,5] with L.start and R.start,
4. concat L=[3,2,1] and R=[5,4,3] with L.start and R.end.

The concatenated result, actually, can be either [1,2,3,4,5] or [5,4,3,2,1]. We choose to keep the left path in the left part in the result, i.e., the output concatenated path would be in order of [1,2,3,4,5].

Related issue number

Fixes #3765