Core: Enable starting of PluginInstallWizard with predefined archive

The wizard usually allows users to chose an archive file path on the
first page. The ExtensionManager would like to first download that
archive and then launch this wizard without said first page.

This change implements such shortcut.

Change-Id: Ifc7ffcc04a59be97bd389697977dbd38714237c7
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/coreplugin/plugininstallwizard.h

@@ -3,6 +3,8 @@
 
 #pragma once
 
+#include <utils/filepath.h>
+
 #include <QCoreApplication>
 
 namespace Core {
@@ -11,7 +13,7 @@ namespace Internal {
 class PluginInstallWizard
 {
 public:
-    static bool exec();
+    static bool exec(const Utils::FilePath &archive = {});
 };
 
 } // namespace Internal