Add a table page object function to get an icon's severity (#2457)

# Pull Request

## 🤨 Rationale

I'd like to be able to verify that icon severities are being set
correctly in the Assets table.

## 👩‍💻 Implementation

Added a new page object function that gets the icon severity for a
particular cell. It is very similar to the existing function for getting
a cell's icon/spinner tag name.

## 🧪 Testing

N/A

## ✅ Checklist

- [x] I have updated the project documentation to reflect my changes or
determined no changes are needed.

---------

Co-authored-by: Milan Raj <rajsite@users.noreply.github.com>

change/@ni-nimble-components-9d9491f3-1f39-4a0b-8196-7d5a25ae3b8f.json

@@ -0,0 +1,7 @@
+{
+  "type": "minor",
+  "comment": "Add a table page object function to get an icon's severity",
+  "packageName": "@ni/nimble-components",
+  "email": "7282195+m-akinc@users.noreply.github.com",
+  "dependentChangeType": "patch"
+}

packages/nimble-components/src/table/testing/table.pageobject.ts

@@ -18,6 +18,7 @@ import { Anchor, anchorTag } from '../../anchor';
 import { tableGroupRowTag, type TableGroupRow } from '../components/group-row';
 import type { Button } from '../../button';
 import { Icon } from '../../icon-base';
+import type { IconSeverity } from '../../icon-base/types';
 import { Spinner, spinnerTag } from '../../spinner';
 import { borderHoverColor } from '../../theme-provider/design-tokens';
 
@@ -207,6 +208,19 @@ export class TablePageObject<T extends TableRecord> {
         return iconOrSpinner.tagName.toLocaleLowerCase();
     }
 
+    public getRenderedMappingColumnCellIconSeverity(
+        rowIndex: number,
+        columnIndex: number
+    ): IconSeverity {
+        const iconOrSpinner = this.getRenderedMappingColumnIconOrSpinner(
+            this.getRenderedCellView(rowIndex, columnIndex)
+        );
+        if (iconOrSpinner instanceof Icon) {
+            return iconOrSpinner.severity;
+        }
+        throw new Error('Cell does not contain an icon');
+    }
+
     public getRenderedGroupHeaderTextContent(groupRowIndex: number): string {
         return (
             this.getGroupRowHeaderView(