stats.lua: add add auto value to vidscale option

This adds auto to vidscale script option, which lets the scale be
inherited from OSD --osd-scale-by-window option.

DOCS/interface-changes/osdscale.txt

@@ -1 +1,2 @@
 change `vidscale` script option type to string for osc.lua
+change `vidscale` script option type to string for stats.lua

DOCS/man/stats.rst

@@ -203,6 +203,8 @@ Configurable Options
 
     Scale the text and graphs with the video.
     ``no`` tries to keep the sizes constant.
+    ``auto`` scales the text and graphs with the OSD, which is scaled with the
+    window or kept at a constant size, depending on the ``--osd-scale-by-window`` option.
 
 Note: colors are given as hexadecimal values and use ASS tag order: BBGGRR
 (blue green red).

player/lua/stats.lua

@@ -60,7 +60,7 @@ local o = {
     shadow_y_offset = 0.0,
     shadow_color = "",
     alpha = "11",
-    vidscale = true,
+    vidscale = "yes",
 
     -- Custom header for ASS tags to style the text output.
     -- Specifying this will ignore the text style values above and just
@@ -1354,9 +1354,16 @@ local function print_page(page, after_scroll)
 end
 
 local function update_scale(_, value)
+    local scale_with_video
+    if o.vidscale == "auto" then
+        scale_with_video = mp.get_property_native("osd-scale-by-window") == true
+    else
+        scale_with_video = o.vidscale == "yes"
+    end
+
     -- Calculate scaled metrics.
     local scale = 1
-    if not o.vidscale and value > 0 then
+    if not scale_with_video and value > 0 then
         scale = 720 / value
     end
     font_size = o.font_size * scale