PluginDialog: set initial focus to filter

Qt Creator provides numbers of plugins.
Setting focus to the filter control helps to find a plugin.

Change-Id: Iac34ff04b97311a8c7890a3cbafdde22b2242dcd
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/coreplugin/plugindialog.cpp

@@ -40,6 +40,7 @@ PluginDialog::PluginDialog(QWidget *parent)
     auto filterLayout = new QHBoxLayout;
     vl->addLayout(filterLayout);
     auto filterEdit = new Utils::FancyLineEdit(this);
+    filterEdit->setFocus();
     filterEdit->setFiltering(true);
     connect(filterEdit, &Utils::FancyLineEdit::filterChanged,
             m_view, &ExtensionSystem::PluginView::setFilter);