osc: usability improvements for pseudo-csd title bar

There are two improvements here:

1) Correct the right-side padding on the title box. This was messed
   up previously because I was passing the title box width when I
   should be passing the x coordinate. I've also increased the
   spacing to separate the title from the window controls more
   clearly.

2) I'ved added a mouse tracking area over the title bar so that the
   osc doesn't disappear if you hover over the title box. This didn't
   work previously because the input area only covers the actual
   window controls. The implementation here is simplified in that
   it's only a mouse area and not an input area. This is enough to
   keep the osc visible, but it won't stop the mouse pointer
   disappearing. Fixing that requires a full input area which, for
   now, I will say isn't worth the effort.

player/lua/osc.lua

@@ -1010,11 +1010,13 @@ function window_controls(topbar)
 
     -- Default alignment is "right"
     local controlbox_left = wc_geo.w - controlbox_w
-    local titlebox_left = wc_geo.x + 5
+    local titlebox_left = wc_geo.x
+    local titlebox_right = wc_geo.w - controlbox_w
 
     if alignment == "left" then
         controlbox_left = wc_geo.x
-        titlebox_left = wc_geo.x + controlbox_w + 5
+        titlebox_left = wc_geo.x + controlbox_w
+        titlebox_right = wc_geo.w
     end
 
     add_area("window-controls",
@@ -1106,12 +1108,19 @@ function window_controls(topbar)
         title = title:gsub("\\n", " "):gsub("\\$", ""):gsub("{","\\{")
         return not (title == "") and title or "mpv"
     end
+    local left_pad = 5
+    local right_pad = 10
     lo = add_layout("wctitle")
     lo.geometry =
-        { x = titlebox_left, y = wc_geo.y - 3, an = 1, w = titlebox_w, h = wc_geo.h }
+        { x = titlebox_left + left_pad, y = wc_geo.y - 3, an = 1,
+          w = titlebox_w, h = wc_geo.h }
     lo.style = string.format("%s{\\clip(%f,%f,%f,%f)}",
         osc_styles.wcTitle,
-        titlebox_left, wc_geo.y - wc_geo.h, titlebox_w, wc_geo.y + wc_geo.h)
+        titlebox_left + left_pad, wc_geo.y - wc_geo.h,
+        titlebox_right - right_pad , wc_geo.y + wc_geo.h)
+
+    add_area("window-controls-title",
+             titlebox_left, 0, titlebox_right, wc_geo.h)
 end
 
 --
@@ -2327,6 +2336,14 @@ function render()
         end
     end
 
+    if osc_param.areas["window-controls-title"] then
+        for _,cords in ipairs(osc_param.areas["window-controls-title"]) do
+            if (mouse_hit_coords(cords.x1, cords.y1, cords.x2, cords.y2)) then
+                mouse_over_osc = true
+            end
+        end
+    end
+
     -- autohide
     if not (state.showtime == nil) and (get_hidetimeout() >= 0) then
         local timeout = state.showtime + (get_hidetimeout()/1000) - now