DevTools: Add heading level 2 role to workspace file system name

The text is bolded and visually represents the start of a workspace
folder mapping so a heading role is appropriate, level 2 was chosen
because the tab heading will be level 1 (https://crrev.com/c/1658659).

Now screen readers can easily jump to a workspace mapping.
NVDA screenshot: https://i.imgur.com/XU8votp.png

This change meets success criteria for WCAG 1.3.1 Info and Relationships.
See: https://www.w3.org/WAI/WCAG21/quickref/#info-and-relationships

Screenshot: https://i.imgur.com/uVZ6xqH.png
Bug: 963183
Change-Id: I4871cc7fe9779c523e7c87089a33d1d12b119e13
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1658641
Commit-Queue: John Emau <johnemau@microsoft.com>
Reviewed-by: Erik Luo <luoe@chromium.org>
Cr-Commit-Position: refs/heads/master@{#676249}

third_party/blink/renderer/devtools/front_end/persistence/WorkspaceSettingsTab.js

@@ -111,7 +111,9 @@ Persistence.WorkspaceSettingsTab = class extends UI.VBox {
     const element = createElementWithClass('div', 'file-system-container');
     const header = element.createChild('div', 'file-system-header');
 
-    header.createChild('div', 'file-system-name').textContent = folderName;
+    const nameElement = header.createChild('div', 'file-system-name');
+    nameElement.textContent = folderName;
+    UI.ARIAUtils.markAsHeading(nameElement, 2);
     const path = header.createChild('div', 'file-system-path');
     path.textContent = fileSystemPath;
     path.title = fileSystemPath;