Add the ability to assign multiple aimpoints on a unit

Currently all units can only accept one aimposition (ussually its in line with the midposition of the unit/building)

there are a number of known to me edge cases where the same unit or building will be in a one way engagements while stationary

https://github.com/beyond-all-reason/Beyond-All-Reason/pull/2897

Start by reviewing the issue context and the linked Beyond All Reason pull request 2897, since no files, tests, or entry points are identified here. The work is done when units and buildings can accept multiple aimpoints, including the stationary one-way engagement cases described in the issue.

Written by the indexing model from the issue text.