Add: [Linux] change default scroll mode to non-mouse-lock (#10920)

Wayland doesn't support mouse warping, X11 only for native
systems (so not for remote desktop, WSLg, etc), and emscripten
neither without complications. All these cannot offer a
mouse-lock.

src/lang/english.txt

@@ -1558,7 +1558,7 @@ STR_CONFIG_SETTING_LINKGRAPH_COLOURS_GREY_TO_RED                :Grey to red
 STR_CONFIG_SETTING_LINKGRAPH_COLOURS_GREYSCALE                  :Greyscale
 
 STR_CONFIG_SETTING_SCROLLMODE                                   :Viewport scroll behaviour: {STRING2}
-STR_CONFIG_SETTING_SCROLLMODE_HELPTEXT                          :Behaviour when scrolling the map
+STR_CONFIG_SETTING_SCROLLMODE_HELPTEXT                          :Behaviour when scrolling the map. The "mouse position locked" options don't work on all systems, like web-based versions, touchscreens, Linux with Wayland, and others
 ###length 4
 STR_CONFIG_SETTING_SCROLLMODE_DEFAULT                           :Move viewport with RMB, mouse position locked
 STR_CONFIG_SETTING_SCROLLMODE_RMB_LOCKED                        :Move map with RMB, mouse position locked

src/table/settings/gui_settings.ini

@@ -98,7 +98,7 @@ strval   = STR_CONFIG_SETTING_AUTOSCROLL_DISABLED
 cat      = SC_BASIC
 
 [SDTC_VAR]
-ifdef    = __EMSCRIPTEN__
+ifdef    = UNIX
 var      = gui.scroll_mode
 type     = SLE_UINT8
 flags    = SF_NOT_IN_SAVE | SF_NO_NETWORK_SYNC | SF_GUI_DROPDOWN
@@ -111,7 +111,7 @@ strval   = STR_CONFIG_SETTING_SCROLLMODE_DEFAULT
 cat      = SC_BASIC
 
 [SDTC_VAR]
-ifndef    = __EMSCRIPTEN__
+ifndef    = UNIX
 var      = gui.scroll_mode
 type     = SLE_UINT8
 flags    = SF_NOT_IN_SAVE | SF_NO_NETWORK_SYNC | SF_GUI_DROPDOWN