Git: show commit given as command line parameter in diff editor

ex: qtcreator -client -git-show d3eb585db9 from qt-creator source dir.

Change-Id: Ice62f062d431d2ab74e3d6832dfc8b0b555dfa19
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: André Hartmann <aha_1980@gmx.de>

src/plugins/git/gitplugin.h

@@ -89,6 +89,9 @@ public:
     void startCommit(CommitType commitType = SimpleCommit);
     void updateBranches(const QString &repository);
 
+    QObject *remoteCommand(const QStringList &options, const QString &workingDirectory,
+                           const QStringList &args) override;
+
 protected:
     void updateActions(VcsBase::VcsBasePlugin::ActionState) override;
     bool submitEditorAboutToClose() override;