Notebooks A11Y: Add button role for Placeholder Links (#15851)

* Add button role

* Add aria-label

* localize aria label

src/sql/workbench/contrib/notebook/browser/cellViews/placeholderCell.component.html

@@ -7,7 +7,7 @@
 <div style="overflow: hidden; width: 100%; height: 100%; display: flex; flex-flow: column">
 	<div class="placeholder-cell-component" style="flex: 0 0 auto;">
 		<div class="placeholder-cell-component text">
-			<p>{{clickOn}} <a id="addCode" href="#" (click)="addCell('code', $event)">{{plusCode}}</a> {{or}} <a id="addMarkdown" href="#" (click)="addCell('markdown', $event)">{{plusText}}</a> {{toAddCell}}</p>
+			<p>{{clickOn}} <a id="addCode" href="#" role="button" [attr.aria-label]=plusCodeAriaLabel (click)="addCell('code', $event)">{{plusCode}}</a> {{or}} <a id="addMarkdown" href="#" role="button" [attr.aria-label]=plusTextAriaLabel (click)="addCell('markdown', $event)">{{plusText}}</a> {{toAddCell}}</p>
 		</div>
 	</div>
 </div>

src/sql/workbench/contrib/notebook/browser/cellViews/placeholderCell.component.ts

@@ -68,6 +68,14 @@ export class PlaceholderCellComponent extends CellView implements OnInit, OnChan
 		return localize('toAddCell', "to add a code or text cell");
 	}
 
+	get plusCodeAriaLabel(): string {
+		return localize('plusCodeAriaLabel', "Add a code cell");
+	}
+
+	get plusTextAriaLabel(): string {
+		return localize('plusTextAriaLabel', "Add a text cell");
+	}
+
 	public addCell(cellType: string, event?: Event): void {
 		if (event) {
 			event.preventDefault();