CityPainter improvements

[elexis]

Proposed improvements for the CityPainter from #5061 used in Jebel Barkal:

• Buildings should face the path, so that (1) spawned units are spawned on the path and don't become trapped between buildings and (2) the city itself looks visually more appealing

• Collision tests should be more precise than 1 terrain tile. As of r21598 we only pass 0 distances between the buildings, but in almost all cases there is at least 1 tile distance between buildings due to the imprecision.

[elexis]

The uploaded patch implements an option to let buildings at the border of the area face towards the border.

This is important for two reasons, in particular on Jebel Barkal:

• Visually: the entrance of the building should be at the path of the city
• Pathfinding bugs when spawning: Units can become trapped between buildings if they aren't spawned on the path at the border of the area.

The patch however has crucial issues:

• Very slow (minutes)
• No more large buildings placed on Jebel Barkal at all, because all buildings are at the border, all buildings have a forced orientation and that doesn't simply fit always.

The patch also fixes a different bug: Only two of the 4 possible 90° angles actually occur as the buildings aren't rotated around their center.

[elexis]

In 21611:

Reduce pathfinding lag on Jebel Barkal a bit by using actor palms in the city (preventing units in formation from becoming locked in at the spawn point).

Preferably, the buildings should be rotated so that they face the path, refs #5090.
Start attacks again in case a player dared to rebuild a CC.
Fix missing negation in rP21609.
Variable naming consistency.

[elexis]

Not rotating buildings correctly means computing 43 paths per turn uselessly per occurrence of the bug: