Add `Expand the border [cityFilter]` Triggerable

[RobLoach]

In Brave New World, the Shoshone found cities with 8 extra owned tiles. By having a unique to allow expanding a city's border, we can accomplish it in a clean way...

"Expand the border [in this city] by [8] <upon founding a city>"

[yairm210]

"expand the border" is not a technical term used elsewhere in the game.

We already have "Gain control over [tileFilter] tiles in a [nonNegativeAmount]-tile radius" so I would change this to "Gain control over [positiveAmount] tiles [cityFilter]"

[SomeTroglodyte]

But the "The cultural cost of acquiring new tiles does not change" aspect won't work.

This is the one thing I'd buy the original for, to get numbers, but there's no DRM free sale, no boxed CD's, and Steam actively blocks certain privacy protections.

I've discussed that a few times over the years (can't find the main arguments, but mentioned in passing in #9065), and still have a local branch (https://github.com/SomeTroglodyte/Unciv/tree/CityTileCost isn't the most recent version) fixing the logic (+ fixing the mistake that citadels and gold buying increase culture cost too, while in Civ5 they don't), but I've never gotten input on how to restore balance, 'cuz IIRC neither our culture nor buy costs match Civ5 exactly. Also, there's an aspect of the original I never got 100% figured out from analyzing the DLL code, namely a "cultural distance"...

Edit: No, not "cultural distance", they called it "influence cost" (that's the buy code, but culture cost had something similar as far as I remember)

Edit: Another, more relevant reference: https://github.com/yairm210/Unciv/pull/10510#issuecomment-1815332760

[RobLoach]

This doesn't do anything with cost. Could you clarify what you're proposing?

[SomeTroglodyte]

Just saying, to emulate the Shoshone "Great Expanse" faithfully you'd be SOL. I thought to Mod the Shoshone long ago, because they're the one BNW civ that's got nothing to do with tourism (OK that's a little simplified), but dropped it as long as the tile acquisition cost calculation is as it is.

[RobLoach]

as long as the tile acquisition cost calculation is as it is

Got it. So the influence cost isn't really handled correctly in Unciv. This doesn't handle anything of that, and just adds the tiles to the city. Hopefully we can clean up the culture cost of owning tiles later on :+1:

change this to "Gain control over [positiveAmount] tiles [cityFilter]"

Done. Added a test too.