[New Feature] Shared Build Limit

[Damfoos]

Description:

Ares introduces a way to convert units into different units once they are promoted, which is quite handy if you want to emulate multi-stage veterancy. While it works pretty good with regular units, units that have build limit can be built again if they are promoted, because technically they don't exist in the game anymore and therefore their existing versions don't count towads the limit. There's a workaround that uses negative prerequisites to avoid that, but as a side effect it removes the unit cameo from the sidebar, which is inconsistent and confusing for some. Therefore, a more clean solution is needed.

Possible Implementation:

The solution to this would be a tag to group multiple units under the same build limit, much like GroupAs makes the game select units of different type if they are coded to be of the same group. This would allow veteran versions of units (assuming they are their own units) to not reset the limit for the rookie versions, as they would still be counted towards it:

[MMKIIVET]
BuildLimit.Share=MMKII ; if MMKIIVET is present in the game, new MMKII cannot be built if the amount of MMKII and MMKIIVET on the field is equal to the BuildLimit of MKII.

Another usercase would be multiple choice build options, like when you are given 3 heroes but can only pick one until it dies. This solution would allow to choose between the options without the side effects of the currently used solution.

[HERO1]
BuildLimit.Share=HERO2, HERO3 ; if HERO1 is present in the game, HERO2 and HERO3 cannot be built, assuming the BuildLimit is 1

I don't know whether each unit of the group should have this tag defined, but it would probably allow for further customization. I don't know what should happen if different units in the group have different BuildLimit, probably some idiot-proof system is needed.