Ensure menu items have non-conflicting accelerators set.

This also changes the "Passwords and autofill" (refresh-only) submenu
item for showing the password manager to the existing string for this.
The difference is that the existing string has branded and non-branded
versions, while the new string does not; I suspect this was an oversight
when adding the new string.

Bug: none
Change-Id: I634f6bcd23ef887f9cecd5b4273c9ee33fc8bd06
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4557224
Reviewed-by: Elaine Chien <elainechien@chromium.org>
Auto-Submit: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Elaine Chien <elainechien@chromium.org>
Code-Coverage: Findit <findit-for-me@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1148766}