CnC map generation previously only supported maps with water/beaches
for the DESERT tileset, as it is the only tileset with a complete set
of beach tiles. This change adds support for the other tilesets
(TEMPERAT, SNOW, WINTER) by adding fake beach templates constructed
from actors and other templates' tiles that look reasonable in both
original and remastered graphics.
This means all CnC tilesets have feature parity in the map generator.
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