MDL-85250 mod_book: Replace hardcoded separator in page titles

* Replace hard-coded ': ' by the usual separator constant in Book

mod/book/index.php

@@ -42,7 +42,7 @@ $strintro        = get_string('moduleintro');
 $strlastmodified = get_string('lastmodified');
 
 $PAGE->set_url('/mod/book/index.php', array('id' => $course->id));
-$PAGE->set_title($course->shortname.': '.$strbooks);
+$PAGE->set_title($course->shortname . \moodle_page::TITLE_SEPARATOR . $strbooks);
 $PAGE->set_heading($course->fullname);
 $PAGE->navbar->add($strbooks);
 echo $OUTPUT->header();

mod/book/view.php

@@ -94,7 +94,7 @@ if ($chapterid == '0') { // Go to first chapter if no given.
 // Prepare header.
 $pagetitle = $book->name;
 if ($chapter = $DB->get_record('book_chapters', ['id' => $chapterid, 'bookid' => $book->id])) {
-    $pagetitle .= ": {$chapter->title}";
+    $pagetitle .= \moodle_page::TITLE_SEPARATOR . $chapter->title;
 }
 
 $PAGE->set_other_editing_capability('mod/book:edit');