Terminal: Add support for copy (OSC52)

Allows terminal apps like vim to set the clipboard, even from inside
an ssh/remote shell.

Change-Id: I1d068737ef65bb4541c3fc9c43870986865f1b45
Reviewed-by: Cristian Adam <cristian.adam@qt.io>

src/plugins/terminal/shellintegration.h

@@ -23,6 +23,8 @@ public:
     void onBell() override;
     void onTitle(const QString &title) override;
 
+    void onSetClipboard(const QByteArray &text) override;
+
     void prepareProcess(Utils::Process &process);
 
 signals: