Layers: Send to Current Layer refuses a hidden or locked current layer

A click on a Layers row runs layer.setCurrent, which makes the row's
layer current whether it is hidden or locked and keeps the selection.
Object › Arrange › Send to Current Layer then moved the selected
objects into that layer, or into a sublayer of a hidden or locked
layer, and left them selected. In that case drawing, typing and
pasting put new art on the topmost layer that is shown and unlocked,
and since #1039 they fail with "the target layer is locked or hidden"
when no layer is shown and unlocked.

Send to Current Layer now fails with that error when the current layer
is hidden or locked, or is inside a hidden or locked layer. It makes
the check that DocState::target_parent makes for new art
(Document::is_editable) before it moves anything or records an undo
step. The objects stay where they are and stay selected. The message
already has a row in the cs, de, es, fr, it, ja, pt-br, ru and uk
catalogs.

Docs: docs/target-app-parity.md.

crates/engine/src/cmd/object.rs

@@ -479,6 +479,11 @@ fn send_to_current_layer(s: &mut Session, _: &Value) -> Result<Value> {
     // Ids are reused after undo: the remembered current layer must still be a layer.
     let st = s.doc()?;
     let layer = st.current_layer().or_else(|| st.doc.default_layer()).ok_or_else(|| EngineError::Other("no current layer".into()))?;
+    // When the current layer is hidden or locked, or is inside a hidden or locked layer, the
+    // command fails with the error that `DocState::target_parent` gives for new art.
+    if !st.doc.is_editable(layer) {
+        return Err(EngineError::Other("the target layer is locked or hidden".into()));
+    }
     // When the selected objects are already the topmost in the current layer, in paint order, the
     // document and its undo history stay as they are.
     if st.doc.children(Some(layer)).is_some_and(|c| c.iter().rev().map(|n| n.id).take(ids.len()).eq(ids.iter().rev().copied())) {