Support attributed strings in TableViewIllustratedEmptyView

This adds a new designated initializer taking an NSAttributedString
as a subtitle, and retains the existing initializer as a convenience. The patch adds a delegate that gets notified when links in the subtitle are tapped.

There are no appearance changes to views currently using this class.
A new empty view (on Password Manager) will use the attributed version
to show a link on the empty state.

Bug: 1335156
Change-Id: Ie087d5ad3fbf2241bea0fed0650840ff2d628a3f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3949794
Reviewed-by: Sergio Collazos <sczs@chromium.org>
Commit-Queue: Ernesto Izquierdo Clua <eic@google.com>
Cr-Commit-Position: refs/heads/main@{#1062082}