TextEditor: bound increase and decreaseFontZoom to a 10% grid

This allows to get back to a 100% font zoom with the keyboard shortcuts
by zooming to an odd zoom factor by other means.

Change-Id: Ie90853367b17c207e9c47fc108b8d6f451e0f838
Reviewed-by: Marcus Tillmanns <marcus.tillmanns@qt.io>

src/plugins/texteditor/texteditor.cpp

@@ -6891,6 +6891,18 @@ static void showZoomIndicator(QWidget *editor, const int newZoom)
                                      Utils::FadingIndicator::SmallText);
 }
 
+void TextEditorWidget::increaseFontZoom()
+{
+    d->clearVisibleFoldedBlock();
+    showZoomIndicator(this, TextEditorSettings::increaseFontZoom());
+}
+
+void TextEditorWidget::decreaseFontZoom()
+{
+    d->clearVisibleFoldedBlock();
+    showZoomIndicator(this, TextEditorSettings::decreaseFontZoom());
+}
+
 void TextEditorWidget::zoomF(float delta)
 {
     d->clearVisibleFoldedBlock();