2023-August-31 - 2.6.14490

Improve logic for choosing default players in battle calc. (#11924)

This attempts to address some regressions from 2.5 where in a number of cases, the chosen sides did not correspond to what the user likely wanted. See https://github.com/triplea-game/triplea/issues/11664 for details.

Some additional tests are added, while others are updated to clarify their intentions and in some cases, provide updated expectations.