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.h

@@ -330,6 +330,7 @@ public:
 
 	v3f getEyePosition() const { return m_base_position + getEyeOffset(); }
 	v3f getEyeOffset() const;
+	float getZoomFOV() const;
 
 	inline Metadata &getMeta() { return m_meta; }