[reports] rendering is more responsive by pulsing progressbar

previously the renderer (html-document object to html-string) would
attempt to update progressbar. However the html-object is a deeply
nested hierarchical object, (length object) is not suitable to
calculate progressbar fraction. Therefore we change update by pulsing
progressbar instead every 2500 loops in html-document, html-table and
html-text renderers.

gnucash/report/html-document.scm

@@ -110,8 +110,6 @@
         (let* ((retval '())
                (push (lambda (l) (set! retval (cons l retval))))
                (objs (gnc:html-document-objects doc))
-               (work-to-do (length objs))
-               (work-done 0)
                (title (gnc:html-document-title doc)))
           ;; compile the doc style
           (gnc:html-style-table-compile (gnc:html-document-style doc)
@@ -144,8 +142,7 @@
           (for-each
            (lambda (child)
                (push (gnc:html-object-render child doc))
-               (set! work-done (+ 1 work-done))
-               (gnc:report-percent-done (* 100 (/ work-done work-to-do))))
+               (gnc:pulse-progress-bar))
            objs)
 
           (when headers?

gnucash/report/html-table.scm

@@ -168,6 +168,7 @@
            (format #f "colspan=\"~a\"" (gnc:html-table-cell-colspan cell))))
     (for-each
      (lambda (child)
+       (gnc:pulse-progress-bar)
        (push (gnc:html-object-render child doc)))
      cell-data)
     (push (gnc:html-document-markup-end doc cell-tag))
@@ -475,6 +476,7 @@
           (push (gnc:html-document-markup-end doc rowmarkup))
           (when rowstyle (gnc:html-document-pop-style doc))
 
+          (gnc:pulse-progress-bar)
           (rowloop (cdr rows) (1+ rownum)))))
     (push (gnc:html-document-markup-end doc "tbody"))
 

gnucash/report/html-text.scm

@@ -202,6 +202,7 @@
     (gnc:html-document-push-style doc (gnc:html-text-style p))
     (for-each 
      (lambda (elt)
+       (gnc:pulse-progress-bar)
        (cond ((procedure? elt)
               (push (elt doc)))
              (#t 

gnucash/report/report-utilities.scm

@@ -623,6 +623,14 @@
       (gnc:warn "report more than 100% finished. " percent))
   (gnc-window-show-progress "" percent))
 
+(define-public gnc:pulse-progress-bar
+  (let ((pulse-idx 0))
+    (lambda ()
+      (set! pulse-idx (1+ pulse-idx))
+      (when (= pulse-idx 2500)
+        (set! pulse-idx 0)
+        (gnc-window-show-progress "" 105)))))
+
 (define (gnc:report-finished)
   (gnc-window-show-progress "" -1))