cli: allow (and ignore) -d flag for jj new

We were discussing whether `jj backout` and `jj duplicate` should
support `-d/-A/-B` just like `jj rebase` does. `jj new` already
accepts `-A/-B` but it does not accept `-d`. It does support `-r`,
however. It seems like `-d` is a better match for `jj new` since it
creates a commit on top. So this patch adds support for that flag
too. I now think `-r` sounds misleading for `jj new`, but I left it in
for now.

cli/src/commands/new.rs

@@ -51,9 +51,10 @@ pub(crate) struct NewArgs {
     /// Parent(s) of the new change
     #[arg(default_value = "@")]
     pub(crate) revisions: Vec<RevisionArg>,
-    /// Ignored (but lets you pass `-r` for consistency with other commands)
-    #[arg(short = 'r', hide = true, action = clap::ArgAction::Count)]
-    unused_revision: u8,
+    /// Ignored (but lets you pass `-d`/`-r` for consistency with other
+    /// commands)
+    #[arg(short = 'd', hide = true, short_alias = 'r',  action = clap::ArgAction::Count)]
+    unused_destination: u8,
     /// The change description to use
     #[arg(long = "message", short, value_name = "MESSAGE")]
     message_paragraphs: Vec<String>,