Move landscape generation functions from misc.js to gaia_terrain.js, refs #4804.

Rename passageMaker to createShallowsPassage to avoid confusion with straightPassageMaker aka PassMaker from Corsica & Sardinia and Pyrenean Sierra.
Remove TILE_CENTERED_HEIGHT_MAP operations in that function from rP12641 that don't do anything.
Add infinite loop protection to getTIPIADBON.
Remove unneeded parentheses, braces, redundancy, whitespace issues, use early return and merge consecutive if-statements with a logical or in these functions.