patch 8.2.4891: Vim help presentation could be better

Problem:    Vim help presentation could be better.
Solution:   Add an imported file for extra Vim help support.  Show highlight
            names in the color they have.

runtime/import/dist/vimhelp.vim

@@ -0,0 +1,21 @@
+vim9script
+
+# Extra functionality for displaying Vim help .
+
+# Called when editing the doc/syntax.txt file
+export def HighlightGroups()
+  var buf: number = bufnr('%')
+  var lnum: number = search('\*highlight-groups\*', 'cn')
+  while getline(lnum) !~ '===' && lnum < line('$')
+    var word: string = getline(lnum)->matchstr('^\w\+\ze\t')
+    if word->hlexists()
+      prop_type_add('help-hl-' .. word, {
+	bufnr: buf,
+	highlight: word,
+	combine: false,
+	})
+      prop_add(lnum, 1, {length: word->strlen(), type: 'help-hl-' .. word})
+    endif
+    ++lnum
+  endwhile
+enddef