VCS: Fix display of diff/show commands in progress bar

In 6ae0e8d2c7 we added 2 arguments that
precede the diff sub-command (-c diff.color=false).

When display name is not set, ShellCommand uses the binary followed by the
first argument, so it now showed "Git -c" instead of "Git Diff".

Change-Id: Ie584837bd87fd529e0cd015025fc3bf1a69d085c
Reviewed-by: André Hartmann <aha_1980@gmx.de>
Reviewed-by: Xiaofeng Wang <wasphin@gmail.com>
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

src/plugins/vcsbase/vcsbasediffeditorcontroller.cpp

@@ -98,6 +98,7 @@ public:
     const QString m_directory;
     QString m_startupFile;
     QString m_output;
+    QString m_displayName;
     QPointer<VcsCommand> m_command;
     QPointer<VcsCommandResultProxy> m_commandResultProxy;
     QFutureWatcher<QList<FileData>> *m_processWatcher = nullptr;
@@ -251,6 +252,7 @@ void VcsBaseDiffEditorController::runCommand(const QList<QStringList> &args, uns
     d->cancelReload();
 
     d->m_command = new VcsCommand(workingDirectory(), d->m_client->processEnvironment());
+    d->m_command->setDisplayName(d->m_displayName);
     d->m_command->setCodec(codec ? codec : EditorManager::defaultTextCodec());
     d->m_commandResultProxy = new VcsCommandResultProxy(d->m_command.data(), d);
     d->m_command->addFlags(flags);
@@ -289,6 +291,11 @@ QString VcsBaseDiffEditorController::startupFile() const
     return d->m_startupFile;
 }
 
+void VcsBaseDiffEditorController::setDisplayName(const QString &displayName)
+{
+    d->m_displayName = displayName;
+}
+
 } // namespace VcsBase
 
 #include "vcsbasediffeditorcontroller.moc"