fix: DH-17730: Fix Proxy Model Undefined Formatter (deephaven#2237)

Fixes https://deephaven.atlassian.net/browse/DH-17730 in Enterprise.
Will need to be cherry picked back to v0.85.
web-client-ui issue is
deephaven#2234

Author: dgodinez-dh

packages/iris-grid/src/IrisGridProxyModel.ts

@@ -436,6 +436,14 @@ class IrisGridProxyModel extends IrisGridModel implements PartitionedGridModel {
       : false;
   }
 
+  get formatter(): Formatter {
+    return this.originalModel.formatter;
+  }
+
+  set formatter(formatter: Formatter) {
+    this.originalModel.formatter = formatter;
+  }
+
   setViewport = (
     top: number,
     bottom: number,