PDF written highlights: fix boxes, trash cached tiles

TileCacheItem: add created_ts property.
Document: manage a tile_cache_validity_ts and ignore
older cached tiles.
This timestamps is updated when highlights are written
as annotations in, or deleted from, the PDF, so we can
get the most current rendered bitmap from MuPDF and
avoid highlight ghosts on old tiles.
Save this timestamp in doc settings so older cached to
disk tiles will also be ignored across re-openings.
Bump base for: mupdf.lua: update frontend pboxes with
MuPDF adjusted ones.

frontend/apps/reader/modules/readerview.lua

@@ -760,6 +760,7 @@ In combination with zoom to fit page, page height, content height, content or co
 end
 
 function ReaderView:onReadSettings(config)
+    self.document:setTileCacheValidity(config:readSetting("tile_cache_validity_ts"))
     self.render_mode = config:readSetting("render_mode") or 0
     local rotation_mode = nil
     local locked = G_reader_settings:isTrue("lock_rotation")
@@ -888,6 +889,7 @@ function ReaderView:onPageGapUpdate(page_gap)
 end
 
 function ReaderView:onSaveSettings()
+    self.ui.doc_settings:saveSetting("tile_cache_validity_ts", self.document:getTileCacheValidity())
     self.ui.doc_settings:saveSetting("render_mode", self.render_mode)
     -- Don't etch the current rotation in stone when sticky rotation is enabled
     local locked = G_reader_settings:isTrue("lock_rotation")