Creates a new QgsProxyStyle subclass of QProxyStyle which
automatically sets the base style to match the current
application style (creating a new QStyle object, since
setting the base style takes ownership). Additionally,
QgsProxyStyle correctly parents the style to a parent
widget, avoiding leaks since calling QWidget::setStyle
doesn't transfer ownership.
Fixes incorrect theme used for layer tree view since
addition of indicator icons.
dfa6b6ae19