Reland "[a11y][Passwords] Move focus to generation popup with screen reader on"

This is a reland of commit fd1e91428ce6d64575218c8c62c9a5fb9902b5a3

The CL got reverted for breaking a browser test. The test was
calling `Show()` twice and on the re-draw the accessibility
kSelected was not being set correctly on the buttons. This CL fixes
that (diff between patchset 1 and 2).

Original change's description:
> [a11y][Passwords] Move focus to generation popup with screen reader on
>
> Following accessibility suggestions reported in the bug the CL
> modifies the password suggestion popup behavior with screen reader on:
> * Places the initial focus on the "Use suggested password" button
> * Removes verbose button accessible descriptions (leaving just the
> labels)
>
> Bug: 378508350
> Change-Id: Ib4d00384377b0291b6061416758ad6de04627438
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6039896
> Reviewed-by: Mohamed Amir Yosef <mamir@chromium.org>
> Commit-Queue: Rafał Godlewski <rgod@google.com>
> Cr-Commit-Position: refs/heads/main@{#1386219}

Bug: 378508350
Change-Id: I1f1e3dd160edf573cf8dd0478b2aedba4ffe8c80
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6037950
Reviewed-by: Mohamed Amir Yosef <mamir@chromium.org>
Commit-Queue: Rafał Godlewski <rgod@google.com>
Cr-Commit-Position: refs/heads/main@{#1386723}