[Mullhet] Add PopupItemId::kTitle.

Titles will be used to separate sections in the password manual
fallback.

Mocks: https://screenshot.googleplex.com/3B7RmtfWJSQpQYp.png

This CL basically reverts the change which deleted this popup
item id: crrev.com/c/5104932

Bug: b/331409076
Change-Id: I6de136a243730844dae4437febecd3b8150e3d77
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5412802


Reviewed-by: Vasilii Sukhanov <vasilii@chromium.org>
Commit-Queue: Timofey Chudakov <tchudakov@google.com>
Reviewed-by: Jihad Hanna <jihadghanna@google.com>
Cr-Commit-Position: refs/heads/main@{#1281830}