Added dual page split setting (#4252)

* Add DualPageSplit option

* remove extra line

* Split double-page into two pages

* Remove !isAnimated check and add (ALPHA) to the label

* Fix missing insert pages

* Pager cleanup

* Add dual split to Webtoon and fix Vertical

* Fix L2R/R2L

* Add comments and refactor code in ImageUtil

* Use a simpler split solution in webtoon mode

Co-authored-by: weng <>
Co-authored-by: Andreas E <andreas.everos@gmail.com>
(cherry picked from commit b5017eebbf)

# Conflicts:
#	app/src/main/java/eu/kanade/tachiyomi/ui/reader/viewer/pager/PagerPageHolder.kt
#	app/src/main/java/eu/kanade/tachiyomi/util/system/ImageUtil.kt

app/src/main/res/values/strings.xml

@@ -252,6 +252,7 @@
 
       <!-- Reader section -->
     <string name="pref_fullscreen">Fullscreen</string>
+    <string name="pref_dual_page_split">Dual page split (ALPHA)</string>
     <string name="pref_cutout_short">Show content in cutout area</string>
     <string name="pref_lock_orientation">Lock orientation</string>
     <string name="pref_page_transitions">Animate page transitions</string>