lib: Add RevsetExpression::filtered().

This allows users to easily filter a commit range by conflicts, which will be needed for `next/prev`
further down in the next commit. Users which benefit from it were also migrated.

cli/src/cli_util.rs

@@ -1418,9 +1418,8 @@ See https://github.com/martinvonz/jj/blob/main/docs/working-copy.md#stale-workin
         // are millions of commits added to the repo, assuming the revset engine can
         // efficiently skip non-conflicting commits. Filter out empty commits mostly so
         // `jj new <conflicted commit>` doesn't result in a message about new conflicts.
-        let conflicts = RevsetExpression::filter(RevsetFilterPredicate::HasConflict).intersection(
-            &RevsetExpression::filter(RevsetFilterPredicate::File(FilesetExpression::all())),
-        );
+        let conflicts = RevsetExpression::filter(RevsetFilterPredicate::HasConflict)
+            .filtered(RevsetFilterPredicate::File(FilesetExpression::all()));
         let removed_conflicts_expr = new_heads.range(&old_heads).intersection(&conflicts);
         let added_conflicts_expr = old_heads.range(&new_heads).intersection(&conflicts);
 

lib/src/revset.rs

@@ -356,6 +356,13 @@ impl RevsetExpression {
         })
     }
 
+    /// Filter all commits by `predicate` in `self`.
+    pub fn filtered(
+        self: &Rc<RevsetExpression>,
+        predicate: RevsetFilterPredicate,
+    ) -> Rc<RevsetExpression> {
+        self.intersection(&RevsetExpression::filter(predicate))
+    }
     /// Commits that are descendants of `self` and ancestors of `heads`, both
     /// inclusive.
     pub fn dag_range_to(