Terminal: Enable TerminalProcessInterface

Adds a new helper app "process_stub" that replaces the previous.
"process_stub_unix/win". The purpose was and is to allow processes
to be "injected" into other hosts apps like terminals while still
being able to control and debug them.

A new base class called "TerminalInterface" is used for both the new
Terminal plugin and the legacy TerminalProcess implementation.

Fixes: QTCREATORBUG-16364
Change-Id: If21273fe53ad545d1a768c17c83db4bf2fd85395
Reviewed-by: Christian Stenger <christian.stenger@qt.io>
Reviewed-by: Jarek Kobus <jaroslaw.kobus@qt.io>
Reviewed-by: hjk <hjk@qt.io>

src/plugins/terminal/terminalwidget.h

@@ -71,10 +71,15 @@ public:
         }
     };
 
+    void setShellName(const QString &shellName);
     QString shellName() const;
 
     Utils::FilePath cwd() const;
     Utils::CommandLine currentCommand() const;
+    std::optional<Utils::Id> identifier() const;
+    QProcess::ProcessState processState() const;
+
+    void restart(const Utils::Terminal::OpenTerminalParameters &openParameters);
 
 signals:
     void started(qint64 pid);
@@ -167,6 +172,7 @@ private:
     std::unique_ptr<ShellIntegration> m_shellIntegration;
 
     QString m_shellName;
+    Utils::Id m_identifier;
 
     QFont m_font;
     QSizeF m_cellSize;