feat(reword): change reword default revset to stack() | @

My justification from Discord https://discord.com/channels/915309546984050709/915309546984050712/1058219879850848276:

> For me, it's usually not a problem to see multiple commit messages; the default being stack() means that I have access to more functionality by default; it would be a good way to introduce the user to that functionality; it matches git submit's default revset, and I usually git reword beforehand

Author: arxanas

git-branchless-opts/src/lib.rs

@@ -455,8 +455,13 @@ pub enum Command {
 
     /// Reword commits.
     Reword {
-        /// Zero or more commits to reword. If not provided, defaults to "HEAD".
-        #[clap(value_parser)]
+        /// Zero or more commits to reword.
+        #[clap(
+            value_parser,
+            default_value = "stack() | @",
+            default_value_if("commit_to_fixup", clap::builder::ArgPredicate::IsPresent, "@"),
+            default_value_if("messages", clap::builder::ArgPredicate::IsPresent, "@")
+        )]
         revsets: Vec<Revset>,
 
         /// Options for resolving revset expressions.

git-branchless-reword/src/lib.rs

@@ -325,13 +325,7 @@ fn resolve_commits_from_hashes<'repo>(
     revsets: Vec<Revset>,
     resolve_revset_options: &ResolveRevsetOptions,
 ) -> eyre::Result<Option<Vec<Commit<'repo>>>> {
-    let hashes = if revsets.is_empty() {
-        vec![Revset("HEAD".to_string())]
-    } else {
-        revsets
-    };
-
-    let commit_sets = match resolve_commits(effects, repo, dag, &hashes, resolve_revset_options) {
+    let commit_sets = match resolve_commits(effects, repo, dag, &revsets, resolve_revset_options) {
         Ok(commit_sets) => commit_sets,
         Err(err) => {
             err.describe(effects)?;