Terminal: Improve keyboard shortcuts and mouse copy/paste

Change-Id: I7e032a48cc55143dd8fb038d74eb71c4ad8badac
Reviewed-by: Marcus Tillmanns <marcus.tillmanns@qt.io>

src/plugins/terminal/terminalwidget.h

@@ -81,6 +81,7 @@ protected:
     void setupFont();
     void setupPty();
     void setupColors();
+    void setupActions();
 
     void writeToPty(const QByteArray &data);
 
@@ -113,6 +114,8 @@ protected:
 
     void flushVTerm(bool force);
 
+    void setSelection(const std::optional<Selection> &selection);
+
 private:
     std::unique_ptr<Utils::QtcProcess> m_process;