FOV: Raise lower limit to avoid zoom-loading of distant world (#7234)

In the client, raise lower limit from 30 to 45 degrees, to avoid server
seeing this as a zoom and loading world beyond the server-set limit.
Add minimum in settingtypes.txt and enforce lower limit when set using
minetest.conf.

In the server, distrust the client-sent FOV if below the heuristic zoom
threshold and use the player object property 'zoom_fov' to check it, to
protect against hacked clients.

src/content_sao.cpp

@@ -1473,3 +1473,8 @@ bool PlayerSAO::getSelectionBox(aabb3f *toset) const
 
 	return true;
 }
+
+float PlayerSAO::getZoomFOV() const
+{
+	return m_prop.zoom_fov;
+}