[CTIS QSF tools] use item name remapping to generate matrix subquestion names in differ

[nmdefries]

In the differ, the names in the list of matrix subquestions should ideally be generated using remapped base question names from item_rename_map.csv. Not doing so could lead to errors in the changelog since we're joining the codebook onto the diffs using the generated matrix subquestion names (for matrix questions).

[nmdefries]

Addressed in #1564