New option for disabling of tinting the right margin area in text editor

Since version 4.14 the right margin of the text editor is tinted. The
fill color corresponds to a darkened editor background color (for light
UI themes), or a lightened background color (for dark themes). However,
the default for most other editors and IDEs is just a single  vertical
line, as was the case in Qt Creator up until version 4.13. The different
colored area may be considered uncommon and irritating by some users.
Therefore, the new checkbox "Tint whole margin area" has been added under the
"Text Editor/Display/Text Wrapping" section in the settings for switching
between <= 4.13 and 4.14+ behavior.

Change-Id: I6761943477738a4c78b97a5f70a19f1ff8a428e5
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/texteditor/texteditor.cpp

@@ -4071,7 +4071,7 @@ void TextEditorWidgetPrivate::paintRightMarginArea(PaintEventData &data, QPainte
     data.rightMargin = QFontMetricsF(q->font()).horizontalAdvance(QLatin1Char('x'))
             * m_visibleWrapColumn
             + data.offset.x() + 4;
-    if (data.rightMargin < data.viewportRect.width()) {
+    if (m_marginSettings.m_tintMarginArea && data.rightMargin < data.viewportRect.width()) {
         const QRectF behindMargin(data.rightMargin,
                                   data.eventRect.top(),
                                   data.viewportRect.width() - data.rightMargin,