The cause of a single light source seemingly being lit without spread
was due to its creation in the +Y mapblock boundary layer during map
generation, which was ignored as the overtop.  This overtop explicitly
needs to be omitted during sunlight propagation, however.  To accomplish
this, Mapgen::calcLighting() was split into separate functions taking
separate parameters.
Additionally, do not diminish light too early during spread.  This fixes the
output inconsistency between Map::updateLighting and Mapgen::calcLighting.

Just Markdown, no variant of it. File name intentionally
not changed to “lua_api.md” because of fear to break references
to that file. The file can still be renamed later.

Use/add stone_surface_max_y to speed-optimise/guide dungeon generation
MgV7: Don't let mountain terrain chop dungeons at mapchunk borders
Make mountain terrain update stone_surface_max_y for caves in mountains

Also rewrite mapgen registration for static initialization

Add minetest.get_mapgen_params()
Deprecate minetest.register_on_mapgen_init()

Fixes #1807: When the server list finishes downloading, the local server
list resets in certain conditions

Also set default height_min/height_max to -31000 and 31000,
respectively, for ore and biomes

Biome API: Add shore top and shore filler nodes, underwater node, water top node. Add water top depth and shore height parameters. Remove water dust node