[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/apps/reader/modules/readerlink.lua

@@ -2,6 +2,7 @@
 ReaderLink is an abstraction for document-specific link interfaces.
 ]]
 
+local BD = require("ui/bidi")
 local ButtonDialogTitle = require("ui/widget/buttondialogtitle")
 local ConfirmBox = require("ui/widget/confirmbox")
 local Device = require("device")
@@ -689,7 +690,8 @@ function ReaderLink:onGoBackLink(show_notification_if_empty)
 end
 
 function ReaderLink:onSwipe(arg, ges)
-    if ges.direction == "east" then
+    local direction = BD.flipDirectionIfMirroredUILayout(ges.direction)
+    if direction == "east" then
         if isSwipeToGoBackEnabled() then
             if #self.location_stack > 0 then
                 -- Remember if location stack is going to be empty, so we
@@ -709,7 +711,7 @@ function ReaderLink:onSwipe(arg, ges)
                 return true
             end
         end
-    elseif ges.direction == "west" then
+    elseif direction == "west" then
         local ret = false
         if isSwipeToFollowNearestLinkEnabled() then
             ret = self:onGoToPageLink(ges, isSwipeIgnoreExternalLinksEnabled(), isFootnoteLinkInPopupEnabled())