Add minetest.get_player_window_information() (#12367)

doc/lua_api.txt

@@ -4972,6 +4972,7 @@ Utilities
           protocol_version = 32,     -- protocol version used by client
           formspec_version = 2,      -- supported formspec version
           lang_code = "fr"           -- Language code used for translation
+
           -- the following keys can be missing if no stats have been collected yet
           min_rtt = 0.01,            -- minimum round trip time
           max_rtt = 0.2,             -- maximum round trip time
@@ -4988,6 +4989,42 @@ Utilities
           --vers_string = "0.4.9-git", -- full version string
           --state = "Active"           -- current client state
       }
+* `minetest.get_player_window_information(player_name)`:
+
+      -- Will only be present if the client sent this information (requires v5.7+)
+      --
+      -- Note that none of these things are constant, they are likely to change during a client
+      -- connection as the player resizes the window and moves it between monitors
+      --
+      -- real_gui_scaling and real_hud_scaling can be used instead of DPI.
+      -- OSes don't necessarily give the physical DPI, as they may allow user configuration.
+      -- real_*_scaling is just OS DPI / 96 but with another level of user configuration.
+      {
+          -- Current size of the in-game render target (pixels).
+          --
+          -- This is usually the window size, but may be smaller in certain situations,
+          -- such as side-by-side mode.
+          size = {
+              x = 1308,
+              y = 577,
+          },
+
+          -- Estimated maximum formspec size before Minetest will start shrinking the
+          -- formspec to fit. For a fullscreen formspec, use a size 10-20% larger than
+          -- this and `padding[-0.01,-0.01]`.
+          max_formspec_size = {
+              x = 20,
+              y = 11.25
+          },
+
+          -- GUI Scaling multiplier
+          -- Equal to the setting `gui_scaling` multiplied by `dpi / 96`
+          real_gui_scaling = 1,
+
+          -- HUD Scaling multiplier
+          -- Equal to the setting `hud_scaling` multiplied by `dpi / 96`
+          real_hud_scaling = 1,
+      }
 
 * `minetest.mkdir(path)`: returns success.
     * Creates a directory specified by `path`, creating parent directories