Revamp the Console Synchronous Writer Example

* Use the 'const' keywords more.
* Split very long lines.
* Remove QT_USE_NAMESPACE macro.
* Update includes to common style.

Task-number: QTBUG-60652
Change-Id: I920ff6f7de9cede2e761cb629ab89945e70254d9
Reviewed-by: André Hartmann <aha_1980@gmx.de>
Reviewed-by: Alex Blasche <alexander.blasche@qt.io>