Ambiguous attachment points selection logic

[AlexeyGirin]

This is follow up for #4530

Background
User is able to create molecules (in micro mode) that contains same leaving groups (Rx) for different atoms but same molecule
At that case we have to introduce rule(s) of selection - which attachment point to use in case of bond operation

Solution
Rule: Simply took first valid attachment point for connection. In example above - R7 number 1 and number 3 are valid APs for connection. So one of them should be selected.

[rrodionov91]

Requirements of initial task changed #4530.
Issue describes impossible scenario in current application state.
Closing as not planned