rmgen SlopeConstraint

[elexis]

It should be possible to paint terrain textures and tileclasses on a given area depending on the slope of the terrain.

Latium, Pyrenean Sierra, Belgian Uplands, Corsica & Sardinia, most likely Caledonian Meadows and Wild Lake have custom recipdes to constrain paintings, which should be unified. This way it will become easier for new maps to make use thereof too.

[elexis]

In 21085:

Implement rmgen SlopeConstraint which is met if the elevation difference is within the given range, fixes #5004.

Add NearTileClassesConstraint that is satisfied when there is a tile marked with the given class in the given range.
Use it for the grass and mountain terrain painting on Pyrenean Sierra.

[elexis]

In 21135:

Red Sea random map replica, based on the original map by _kali created in rP18523 deleted in rP20362, refs #4816, #5018, D957.

Uses an unadulterated, easily exchangeable, well compressed topography image of the NASA Blue Marble series in the public domain,
instead of a heavily tuned and not so well licensed NASA SRTM v4.1 image encoded in JSON.
Circular intead of a square map shape.
Randomized, height- and slope-based terrain texture painting, refs #5004.

[elexis]

In 21300:

Ambush bluffs rework.
Remove ugly large circle patterns around the playerbase on Ambush, fixes #4993.
To ensure passability, create ramps from the playerbase to the bluffs.

Change the circular player avoidance to a ChainPlacer generating more heterogenous pattern.
Use vectors in rmgen2 bluffs creation and simplify equations, refs #4992.
Don't turn inaccessible bluffs to plateaus but don't place them until it is certain they are passable.

Increase minimum distance from the playerbase to the mapcenter by picking different distance values per playerbase pattern in g_PlayerbaseTypes.
Attempt to improve bluffs performance by avoiding bluffIgnore by 0 instead of bluff by 12, refs #5011.
Implement AdjacentToAreaConstraint and deleteTerrainEntity.
Delete createBoundingBox and use getBoundingBox, refs #4947, #4805.
Delete fadeToGround and nextToFeature and use conventional createArea calls with the SmoothingPainter of rP21175, refs #5027.
Paint bluff cliffs slightly more accurately using the SlopeConstraint from rP21085, refs #5004.