[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/readergesture.lua

@@ -1,3 +1,4 @@
+local BD = require("ui/bidi")
 local ConfirmBox = require("ui/widget/confirmbox")
 local DataStorage = require("datastorage")
 local Device = require("device")
@@ -225,6 +226,44 @@ function ReaderGesture:init()
     }
     local gm = G_reader_settings:readSetting(self.ges_mode)
     if gm == nil then G_reader_settings:saveSetting(self.ges_mode, {}) end
+
+    -- Some of these defaults need to be reversed in RTL mirrored UI,
+    -- and as we set them in the saved gestures, we need to reset them
+    -- to the defaults in case of UI language's direction change.
+    local mirrored_if_rtl = {
+        tap_top_left_corner = "tap_top_right_corner",
+        tap_right_bottom_corner = "tap_left_bottom_corner",
+    }
+    local is_rtl = BD.mirroredUILayout()
+    if is_rtl then
+        for k, v in pairs(mirrored_if_rtl) do
+            self.default_gesture[k], self.default_gesture[v] = self.default_gesture[v], self.default_gesture[k]
+        end
+    end
+    -- We remember the last UI direction gestures were made on. If it changes,
+    -- reset the mirrored_if_rtl ones to the default for the new direction.
+    local ges_dir_setting = self.ges_mode.."ui_lang_direction_rtl"
+    local prev_lang_dir_rtl = G_reader_settings:isTrue(ges_dir_setting)
+    if (is_rtl and not prev_lang_dir_rtl) or (not is_rtl and prev_lang_dir_rtl) then
+        local reset = false
+        for k, v in pairs(mirrored_if_rtl) do
+            -- We only replace them if they are still the other direction's default.
+            -- If not, the user has changed them: let him deal with setting new ones if needed.
+            if gm[k] == self.default_gesture[v] then
+                gm[k] = self.default_gesture[k]
+                reset = true
+            end
+            if gm[v] == self.default_gesture[k] then
+                gm[v] = self.default_gesture[v]
+                reset = true
+            end
+        end
+        if reset then
+            logger.info("UI language direction changed: resetting some gestures to direction default")
+        end
+        G_reader_settings:flipNilOrFalse(ges_dir_setting)
+    end
+
     self.ui.menu:registerToMainMenu(self)
     self:initGesture()
 end
@@ -1577,8 +1616,12 @@ function ReaderGesture:onToggleReadingOrder()
     local document_module = self.ui.document.info.has_pages and self.ui.paging or self.ui.rolling
     document_module.inverse_reading_order = not document_module.inverse_reading_order
     document_module:setupTouchZones()
+    local is_rtl = BD.mirroredUILayout()
+    if document_module.inverse_reading_order then
+        is_rtl = not is_rtl
+    end
     UIManager:show(Notification:new{
-        text = document_module.inverse_reading_order and _("RTL page turning.") or _("LTR page turning."),
+        text = is_rtl and _("RTL page turning.") or _("LTR page turning."),
         timeout = 2.5,
     })
     return true