PDF text selection: fix/tweak spacing between words/boxes

We may get multiple boxes when selecting texts, one for each
word, and we have to add spaces between the extracted words
ourselves. Previously, we were only adding a space if the
last char of previous word was ASCII, so missing spaces
after accents or greek words.
Try to do better by measuring the distances between boxes
and comparing to box heights, with a few heuristics.

frontend/apps/reader/modules/readerhighlight.lua

@@ -1287,16 +1287,20 @@ function ReaderHighlight:onUnhighlight(bookmark_item)
         sel_pos0 = self.selected_text.pos0
     end
     if self.ui.document.info.has_pages then -- We can safely use page
+        -- As we may have changed spaces and hyphens handling in the extracted
+        -- text over the years, check text identities with them removed
+        local sel_text_cleaned = sel_text:gsub("[ -]", ""):gsub("\xC2\xAD", "")
         for index = 1, #self.view.highlight.saved[page] do
             local highlight = self.view.highlight.saved[page][index]
             -- pos0 are tables and can't be compared directly, except when from
             -- DictQuickLookup where these are the same object.
             -- If bookmark_item provided, just check datetime
-            if highlight.text == sel_text and (
-                    (datetime == nil and highlight.pos0 == sel_pos0) or
-                    (datetime ~= nil and highlight.datetime == datetime)) then
-                idx = index
-                break
+            if ( (datetime == nil and highlight.pos0 == sel_pos0) or
+                 (datetime ~= nil and highlight.datetime == datetime) ) then
+                if highlight.text:gsub("[ -]", ""):gsub("\xC2\xAD", "") == sel_text_cleaned then
+                    idx = index
+                    break
+                end
             end
         end
     else -- page is a xpointer