title: Qt's QFontMetrics::horizontalAdvance() missing for Code Editor Implementation
body: <p>I'm implementing a code editor for a simple scripting language and have been using the Qt Code Editor Example (<a href="http://doc.qt.io/qt-5/qtwidgets-widgets-codeeditor-example.html" rel="noreferrer">http://doc.qt.io/qt-5/qtwidgets-widgets-codeeditor-example.html</a>) as a guide for implementing a QPlainTextEdit with line numbers. The example uses the base widget's fontMetrics() method 'horizontalAdvance' to query the width (or better the advance) of a single character. </p>
  
  <p>The method <code>QFontMetrics::horizontalAdvance(QChar)</code> (see <a href="http://doc.qt.io/qt-5/qfontmetrics.html#horizontalAdvance-1" rel="noreferrer">http://doc.qt.io/qt-5/qfontmetrics.html#horizontalAdvance-1</a>) can be found in the Qt documentation <strong>but my implementation seems to be missing this method</strong>.</p>
  
  <p>I am using Qt 5.10.1 'msvc2017_64' on Windows 10 with Visual Studio Enterprise 2017 Version 15.7.3. I have searched the headers for the missing method, but only found <code>QTextLine::horizontalAdvance()</code> which is not what I need.</p>
  
  <p>I have replaced the <code>QFontMetrics::horizontalAdvance(QChar)</code> call with a call to <code>QFontMetrics::width(QChar)</code> which is working with my current font (Consolas) but I am not sure if its ok for every possible font.</p>
  
  <p>Question 1) Has QFontMetrics::horizontalAdvance() been removed from current version of Qt, is my installation buggy or have I missed something?</p>
  
  <p>Question 2) What is the correct way of getting the advance for a specific (non propotional) font?</p>
  
  <p>Thank you for reading this and trying to help!</p>