cli branch create/set: add --to aliases for -r

Now that `jj move` does not accept `-r` (since it has `--from` and `--to`), `jj set --to` seems more useful
than `jj set -r`.

I am not sure whether `-r` should be kept or removed.

I was also considering adding `create --to` as alias for `create -r`,
but I am hoping `--at` will be easy enough to remember since it's the
preposition one would think of.

cli/src/commands/branch/create.rs

@@ -25,7 +25,7 @@ use crate::ui::Ui;
 #[derive(clap::Args, Clone, Debug)]
 pub struct BranchCreateArgs {
     /// The branch's target revision
-    #[arg(long, short)]
+    #[arg(long, short, visible_alias = "at")]
     revision: Option<RevisionArg>,
 
     /// The branches to create

cli/src/commands/branch/set.rs

@@ -25,7 +25,7 @@ use crate::ui::Ui;
 #[derive(clap::Args, Clone, Debug)]
 pub struct BranchSetArgs {
     /// The branch's target revision
-    #[arg(long, short)]
+    #[arg(long, short, visible_alias = "to")]
     revision: Option<RevisionArg>,
 
     /// Allow moving the branch backwards or sideways