[CRe] Ensure toggling nightmode invalidates the drawCurrentView cache (#6854)

* Use a CRe set* method when toggling nightmode

This ensures it gets flagged as add_reset by the call cache, and that
CRe will actually re-render, as it's necessary if nightmode_images is
enabled (the default).

Fix #6845

* Prevent ReaderHighlight:onTap from running ReaderHighlight:clear when
it's unnecessary.

Avoiding a clearSelection call in CRe that could invalidate the cache
and cause unnecessary redraws.

* Don't store empty highlight arrays when all HLs on a page have
been deleted

frontend/document/credocument.lua

@@ -25,6 +25,7 @@ local CreDocument = Document:new{
     _view_mode = nil,
     _smooth_scaling = false,
     _nightmode_images = true,
+    _nightmode = false,
 
     line_space_percent = 100,
     default_font = "Noto Serif",
@@ -423,7 +424,7 @@ function CreDocument:drawCurrentView(target, x, y, rect, pos)
 
     --local start_ts = FFIUtil.getTimestamp()
     self._drawn_images_count, self._drawn_images_surface_ratio =
-        self._document:drawCurrentPage(self.buffer, self.render_color, Screen.night_mode and self._nightmode_images, self._smooth_scaling, Screen.sw_dithering)
+        self._document:drawCurrentPage(self.buffer, self.render_color, self._nightmode and self._nightmode_images, self._smooth_scaling, Screen.sw_dithering)
     --local end_ts = FFIUtil.getTimestamp()
     --print(string.format("CreDocument:drawCurrentView: Rendering took %9.3f ms", (end_ts - start_ts) * 1000))
 
@@ -877,6 +878,11 @@ function CreDocument:setNightmodeImages(toggle)
     self._nightmode_images = toggle
 end
 
+function CreDocument:setNightMode(toggle)
+    logger.dbg("CreDocument: set nightmode", toggle)
+    self._nightmode = toggle
+end
+
 function CreDocument:setFloatingPunctuation(enabled)
     --- @fixme occasional segmentation fault when toggling floating punctuation
     logger.dbg("CreDocument: set floating punctuation", enabled)