GitGrep: Do not access global state from non-main thread

- VcsCommand calls into VcsOutputWindow at construction, so we need to
  construct it in the main thread
- VcsCommand may not call into global settings from runCommand, so we
  need to store the ssh prompt command
- accessing the GitClient singleton in a non-main thread is not
  thread-safe

Change-Id: I3dcdff8091c2dcea1c165ce5b3eca5ef62d474fd
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Jarek Kobus <jaroslaw.kobus@qt.io>
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/vcsbase/vcscommand.cpp

@@ -43,6 +43,7 @@ VcsCommand::VcsCommand(const QString &workingDirectory, const Environment &envir
     VcsOutputWindow::setRepository(workingDirectory);
     setDisableUnixTerminal();
     m_outputWindow = VcsOutputWindow::instance();
+    m_sshPrompt = VcsBase::sshPrompt();
 
     connect(this, &VcsCommand::started, this, [this] {
         if (flags() & ExpectRepoChanges)
@@ -57,7 +58,7 @@ VcsCommand::VcsCommand(const QString &workingDirectory, const Environment &envir
 const Environment VcsCommand::processEnvironment() const
 {
     Environment env = Core::ShellCommand::processEnvironment();
-    VcsBase::setProcessEnvironment(&env, flags() & ForceCLocale, VcsBase::sshPrompt());
+    VcsBase::setProcessEnvironment(&env, flags() & ForceCLocale, m_sshPrompt);
     return env;
 }
 

src/plugins/vcsbase/vcscommand.h

@@ -63,6 +63,7 @@ private:
 
     void coreAboutToClose() override;
 
+    QString m_sshPrompt;
     bool m_preventRepositoryChanged;
     VcsOutputWindow *m_outputWindow = nullptr;
 };