Fix bug #22650: nontranslatable strings displayed in tooltips for terrain icons

The string for the tooltip of the terrain icon was the
underlying terrain id (same string as the one used to
retreive the image). "gamemap::get_terrain_string"
method is used as string for the tooltip in order to have
a correct translatable string.
Merge branch 'NontransStrTooltipTerrainIcon' of https://github.com/LovCAPONE/wesnoth into LovCAPONE-NontransStrTooltipTerrainIcon

Conflicts:
	changelog
Merge branch 'LovCAPONE-NontransStrTooltipTerrainIcon'