fix: Expose layoutHints in JS API for TreeTable (#5555)

- You could set layout hints in Groovy, but they were not accessible through the JS API
- Required for DH-17076

web/client-api/src/main/java/io/deephaven/web/client/api/tree/JsTreeTable.java

@@ -359,6 +359,7 @@ private enum RebuildStep {
     private Column rowExpandedCol;
     private final Column actionCol;
     private final JsArray<Column> groupedColumns;
+    private JsLayoutHints layoutHints;
 
     // The source JsTable behind the original HierarchicalTable, lazily built at this time
     private final JsLazy<Promise<JsTable>> sourceTable;
@@ -1082,6 +1083,25 @@ public String getDescription() {
         return tableDefinition.getAttributes().getDescription();
     }
 
+    @JsProperty
+    @JsNullable
+    public JsLayoutHints getLayoutHints() {
+        if (layoutHints == null) {
+            createLayoutHints();
+        }
+        return layoutHints;
+    }
+
+    private void createLayoutHints() {
+        String hintsString = tableDefinition.getAttributes().getLayoutHints();
+        JsLayoutHints jsHints = new JsLayoutHints();
+        if (hintsString == null) {
+            layoutHints = null;
+        } else {
+            layoutHints = jsHints.parse(hintsString);
+        }
+    }
+
     /**
      * The current number of rows given the table's contents and the various expand/collapse states of each node. (No
      * totalSize is provided at this time; its definition becomes unclear between roll-up and tree tables, especially