feat(nodejs): expose computed columns and refreshColumn

addComputedColumns declares columns defined by a SQL expression, and
refreshColumn fills a computed column's unfilled rows:

    await table.addComputedColumns([{ name: "doubled", valueSql: "x * 2" }]);
    await table.refreshColumn("doubled");

docs/src/js/interfaces/RefreshColumnResult.md

@@ -0,0 +1,23 @@
+[**@lancedb/lancedb**](../README.md) • **Docs**
+
+***
+
+[@lancedb/lancedb](../globals.md) / RefreshColumnResult
+
+# Interface: RefreshColumnResult
+
+## Properties
+
+### rowsFilled
+
+```ts
+rowsFilled: number;
+```
+
+***
+
+### version
+
+```ts
+version: number;
+```