Spawn a possibly interactive subshell.
        Args:
            context:_file File that must be sourced in the new shell, this
                configures the Rez environment.
            tmpdir: Tempfiles, if needed, should be created within this path.
            rcfile: Custom startup script.
            norc: Don't run startup scripts. Overrides rcfile.
            stdin: If True, read commands from stdin in a non-interactive shell.
                If a different non-False value, such as subprocess.PIPE, the same
                occurs, but stdin is also passed to the resulting subprocess.Popen
                object.
            command: If not None, execute this command in a non-interactive shell.
                If an empty string, don't run a command, but don't open an
                interactive shell either.
            env: Environ dict to execute the shell within; uses the current
                environment if None.
            quiet: If True, don't show the configuration summary, and suppress
                any stdout from startup scripts.
            pre_command: Command to inject before the shell command itself. This
                is for internal use.
            add_rez: If True, assume this shell is being used with rez, and do
                things such as set the prompt etc.
            package_commands_sourced_first: If True, source the context file before
                sourcing startup scripts (such as .bashrc). If False, source
                the context file AFTER. If None, use the configured setting.
            popen_args: args to pass to the shell process object constructor.

        Returns:
            A subprocess.Popen object representing the shell process.

def spawn_shell(self, context_file, tmpdir, rcfile=None, norc=False,
                    stdin=False, command=None, env=None, quiet=False,
                    pre_command=None, add_rez=True,
                    package_commands_sourced_first=None, **Popen_args):
        """Spawn a possibly interactive subshell.
        Args:
            context:_file File that must be sourced in the new shell, this
                configures the Rez environment.
            tmpdir: Tempfiles, if needed, should be created within this path.
            rcfile: Custom startup script.
            norc: Don't run startup scripts. Overrides rcfile.
            stdin: If True, read commands from stdin in a non-interactive shell.
                If a different non-False value, such as subprocess.PIPE, the same
                occurs, but stdin is also passed to the resulting subprocess.Popen
                object.
            command: If not None, execute this command in a non-interactive shell.
                If an empty string, don't run a command, but don't open an
                interactive shell either.
            env: Environ dict to execute the shell within; uses the current
                environment if None.
            quiet: If True, don't show the configuration summary, and suppress
                any stdout from startup scripts.
            pre_command: Command to inject before the shell command itself. This
                is for internal use.
            add_rez: If True, assume this shell is being used with rez, and do
                things such as set the prompt etc.
            package_commands_sourced_first: If True, source the context file before
                sourcing startup scripts (such as .bashrc). If False, source
                the context file AFTER. If None, use the configured setting.
            popen_args: args to pass to the shell process object constructor.

        Returns:
            A subprocess.Popen object representing the shell process.
        """
        raise NotImplementedError