Add option to flash white screen on page change in reader for e-ink displays

Closes #2123

(cherry picked from commit 443d56f69bc1df515ed2edcd5b2936ed8710fb71)

# Conflicts:
#	app/src/main/java/eu/kanade/presentation/more/settings/screen/SettingsReaderScreen.kt
#	app/src/main/java/eu/kanade/presentation/reader/settings/GeneralSettingsPage.kt
#	app/src/main/java/eu/kanade/tachiyomi/ui/reader/ReaderActivity.kt

app/src/main/java/eu/kanade/presentation/reader/settings/GeneralSettingsPage.kt

@@ -88,7 +88,14 @@ internal fun ColumnScope.GeneralPage(screenModel: ReaderSettingsScreenModel) {
     /*CheckboxItem(
         label = stringResource(R.string.pref_page_transitions),
         pref = screenModel.preferences.pageTransitions(),
-    )*/
+    ) SY <-- */
+
+    CheckboxItem(
+        label = stringResource(R.string.pref_flash_page),
+        pref = screenModel.preferences.flashOnPageChange(),
+    )
+
+    // SY -->
     CheckboxItem(
         label = stringResource(R.string.auto_webtoon_mode),
         pref = screenModel.preferences.useAutoWebtoon(),