[RTL UI] update widgets and apps for UI mirroring

Small tweaks all around to handle UI mirroring:
- swap existing symbols like arrows, or use alternative ones
- rotate some images, like chevrons and dogear icons
- flip some left and right swipe handling
- flip some geometry arithmetic like tap on left or right
  side of page or dict window
- use new ProgressWidget:getPercentageFromPosition() instead
  of geometry arithmetic
- BD.wrap() some concatenated string bits, like in reader
  and menu footers
- flip inverse_reading_order when UI is mirrored

More specific tweaks:
- ReaderGesture: reset some specific gestures when UI direction
  has changed (tap on top/bottom left/right corners, for
  bookmarks and FileManager "Plus menu").
- ReaderRolling: show markers on the correct side of page,
  in single or dual page mode.
- KoptOptions: swap left and right icons in Alignment toggle
- CheckMark: proper rendering in all 4 mirroring/rtl combinations.
- VirtualKeyboard: forbid any mirroring
- Move util.getMenuText into Menu.lua

frontend/ui/widget/closebutton.lua

@@ -34,11 +34,11 @@ function CloseButton:init()
         face = Font:getFace("cfont", 30),
     }
 
+    -- The text box height is greater than its width, and we want this × to be
+    -- diagonally aligned with the top right corner (assuming padding_right=0,
+    -- or padding_right = padding_top so the diagonal aligment is preserved).
     local text_size = text_widget:getSize()
-    -- The text box height is greater than its width, and we want this × to
-    -- be diagonally aligned with our top right border
     local text_width_pad = (text_size.h - text_size.w) / 2
-    -- We also add the provided padding_right
 
     self[1] = FrameContainer:new{
         bordersize = 0,