Add upon liberating a city trigger

[Fanfblrik]

Summary

• Engine support for RekMOD Romania (Golden Age points on liberate).
• New trigger: upon liberating [cityFilter] cities (UniqueTarget.TriggerCondition).
• Fired at the end of CityConquestFunctions.liberateCity for the liberating civ, filtered against the liberated city (e.g. [any]).
• any accepted as a cityFilter (alongside all/All) so the phrasing reads naturally.
• Compose as Instantly gain [N] [Golden Age points] <upon liberating [any] cities>.

Test plan

• Civ with liberate GAP unique: liberate a city → GAP granted once.
• Narrower filter only fires for matching liberated cities.
• Conquer/puppet/annex without liberate → this trigger does not fire.
• Existing conquer triggers unchanged.

[yairm210]

Add cityfilter

[yairm210]

"Upon liberating cityFilter cities" to make it parse well with "any"

[Fanfblrik]

Done — trigger is now upon liberating [cityFilter] cities, matched against the liberated city (so [any] reads naturally). Also accepted any as a cityFilter synonym for all/All.

[Fanfblrik]

Motivation: RekMOD Romania UA — Golden Age points on liberating a city (Gain … <upon liberating [any] cities>).