Make chat web links clickable (#11092)

If enabled in minetest.conf, provides colored, clickable (middle-mouse or ctrl-left-mouse) weblinks in chat output, to open the OS' default web browser.

builtin/settingtypes.txt

@@ -973,6 +973,12 @@ mute_sound (Mute sound) bool false
 
 [Client]
 
+#    Clickable weblinks (middle-click or ctrl-left-click) enabled in chat console output.
+clickable_chat_weblinks (Chat weblinks) bool false
+
+#    Optional override for chat weblink color.
+chat_weblink_color (Weblink color) string
+
 [*Network]
 
 #    Address to connect to.