DevTools: Add heading level 2 role to workspace file system name
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 <eb1ab95229dc4a7075d47452a0619cbd5cff6c28@microsoft.com>
Reviewed-by: Erik Luo <26192f5e05d23e5ee959014fb911d780e566545b@chromium.org>
Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#676249}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 97809688209693dff107199935e8bef0e2a2d0a2

ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend