Context: #12532 (comment)

JabRef does not support \ to be used as escaping for the keyword separator

Task:

1. Add test cases for \, in org.jabref.model.entry.KeywordListTest
2. Adapt org.jabref.model.entry.KeywordList#parse(java.lang.String, java.lang.Character, java.lang.Character) to implement the escaping

There is code proposed - with good test cases https://github.com/JabRef/jabref/pull/12888/files#diff-405010f9d24d966c1c8d319857c458e7a81761922448a5ff981e645d4ad43efc.

However, the review comments were not addressed. --> When working on this address #12888 (comment)