Support DAP's `restart` request if the program is started with `rdbg` executable

[st0012]

Your proposal

When a remote debuggee is started by the rdbg executable, like rdbg -c -- <cmd>, we can record the <cmd> and use it for the DAP's restart request.

[ko1]

Maybe we need to restore the ENV but using exec(2) I'm not sure we can implement restart command. Restarting by extension can be considered but not sure now.