This implementations provides a Line Number Area for the code editor
in the GUI and Highlight to current line.
It was created a custom widget that inherits from QPlainTextEdit. It works
like a code editor with syntax highlighter.
In the LineNumberArea class that inherits from QWidget the paintEvent
invokes
the draw event in CodeEditor class.
The CodeEditor class knows the LineNumberArea by composition for while.
Fixes T4551
Ref T1625