Misc: Get rid of the legacy defaults.lua globals (#9546)

* This removes support for the following deprecated constants: `DTAP_ZONE_FLIPPING`, `DTAP_ZONE_BOOKMARK`, `DCREREADER_CONFIG_DEFAULT_FONT_GAMMA`
* The "Advanced settings" panel now highlights modified values in bold (think about:config in Firefox ;)).
* LuaData: Isolate global table lookup shenanigans, and fix a few issues in unused-in-prod codepaths.
* CodeStyle: Require module locals for Lua/C modules, too.
* ScreenSaver: Actually garbage collect our widget on close (ScreenSaver itself is not an instantiated object).
* DateTimeWidget: Code cleanups to ensure child widgets can be GC'ed.

frontend/apps/reader/modules/readerrolling.lua

@@ -9,6 +9,7 @@ local ReaderPanning = require("apps/reader/modules/readerpanning")
 local Size = require("ui/size")
 local UIManager = require("ui/uimanager")
 local bit = require("bit")
+local lfs = require("libs/libkoreader-lfs")
 local logger = require("logger")
 local time = require("ui/time")
 local _ = require("gettext")
@@ -152,6 +153,7 @@ function ReaderRolling:onReadSettings(config)
     self.ui.document:requestDomVersion(config:readSetting("cre_dom_version"))
     -- If we're using a DOM version without normalized XPointers, some stuff
     -- may need tweaking:
+    local cre = require("document/credocument"):engineInit()
     if config:readSetting("cre_dom_version") < cre.getDomVersionWithNormalizedXPointers() then
         -- Show some warning when styles "display:" have changed that
         -- bookmarks may break