BookMap on devices with useDPadAsActionKeys (#11916)

as first discussed here #11908. This PR brings the book map to non-touch devices that useDPadAsActionKeys().

Book map can be accessed from the menu or by using the following shortcut: ScreenKB + Down or Shift + Down depending on whether you use a K4 device or a kindle with keyboard respectively.

Inside the book map, a user can toggle the hamburger menu by pressing the Menu key and make any adjustment from there. ScreenKB (or Shift) + Up/Down allows it to scroll and Page turn buttons to move by whole full page turns. Back key allows user to exit the map.

frontend/apps/reader/modules/readerthumbnail.lua

@@ -21,10 +21,12 @@ local _ = require("gettext")
 local ReaderThumbnail = WidgetContainer:extend{}
 
 function ReaderThumbnail:init()
-    if not Device:isTouchDevice() then
+    self:registerKeyEvents()
+    if not Device:isTouchDevice() and not Device:useDPadAsActionKeys() then
         -- The BookMap and PageBrowser widgets depend too much on gestures,
-        -- making them work with keys would be hard and very limited, so
+        -- making them work with not enough keys on Non-Touch would be hard and very limited, so
         -- just don't make them available.
+        -- We will only let BookMap run on useDPadAsActionKeys devices.
         return
     end
 
@@ -62,6 +64,16 @@ function ReaderThumbnail:init()
     end
 end
 
+function ReaderThumbnail:registerKeyEvents()
+    if Device:hasDPad() and Device:useDPadAsActionKeys() then
+        if Device:hasKeyboard() then
+            self.key_events.ShowBookMap = { { "Shift", "Down" } }
+        else
+            self.key_events.ShowBookMap = { { "ScreenKB", "Down" } }
+        end
+    end
+end
+
 function ReaderThumbnail:addToMainMenu(menu_items)
     menu_items.book_map = {
         text = _("Book map"),
@@ -75,6 +87,8 @@ function ReaderThumbnail:addToMainMenu(menu_items)
             self:onShowBookMap(true)
         end,
     }
+    -- PageBrowser still needs some work before we can let it run on non-touch devices with useDPadAsActionKeys
+    if Device:hasDPad() and Device:useDPadAsActionKeys() then return end
     menu_items.page_browser = {
         text = _("Page browser"),
         callback = function()