fix(data-table): use friendly name for csv header (#710)

Author: kaseyhinton

packages/leavittbook/src/demos/titanium-data-table-core-demo.ts

@@ -290,6 +290,7 @@ export class TitaniumDataTableCoreDemo extends LitElement {
         key: 'MaxSpeed',
         render: (item) => html`${item.MaxSpeed} mph`,
         width: '250px',
+        friendlyName: 'Max Speed',
       },
       {
         key: 'IsElectric',

packages/web/titanium/data-table/data-table-core.ts

@@ -588,7 +588,8 @@ export class TitaniumDataTableCore<T extends object> extends LoadWhile(LitElemen
                               this.items.map((item) => {
                                 const itemData = {};
                                 for (const metaData of currentlyShownColumnMetaData) {
-                                  itemData[metaData.key] = metaData.csvValue ? metaData.csvValue(item) : item[metaData.key];
+                                  const header = metaData.friendlyName ?? metaData.key;
+                                  itemData[header] = metaData.csvValue ? metaData.csvValue(item) : item[metaData.key];
                                 }
                                 return itemData;
                               }) ?? [];