Backmerge: #1773 Save to CDX converts plus and arrow into lone pair and line

[AliaksandrDziarkach]

Fix kCDXProp_Arrow_ArrowHead values. Fix UTs

Backmerge request

• [ ] PR name follows the pattern Backmerge: #1234 – issue name
• [ ] PR is linked with the issue
• [ ] base branch (master or release/xx) is correct
• [ ] code contains only backmerge changes