Reland "[FedCM] Implement modal verifying sheet"

This reverts commit 135a8f032597f1d9105ee6af9215eb49287c9866.

Reason for revert: Tests are fixed

Original change's description:
> Revert "[FedCM] Implement modal verifying sheet"
>
> This reverts commit 39f5b1d4da7a7ddb682a30cd55383c3d2554c3d1.
>
> Reason for revert: Failing tests on linux-ubsan-vptr
> https://ci.chromium.org/ui/p/chromium/builders/ci/linux-ubsan-vptr/28612/overview
>
> Original change's description:
> > [FedCM] Implement modal verifying sheet
> >
> > When ShowVerifyingSheet is called in a modal FedCM dialog, a progress
> > bar is added at the very top of the dialog and the buttons are disabled.
> >
> > Screenshot
> > https://issues.chromium.org/action/issues/41491333/attachments/53846790?download=false
> >
> > Bug: 41491333
> > Change-Id: I10f106019350d16c3a97cec3d87af687fae600f0
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5314683
> > Commit-Queue: Christian Biesinger <cbiesinger@chromium.org>
> > Auto-Submit: Zachary Tan <tanzachary@chromium.org>
> > Reviewed-by: Christian Biesinger <cbiesinger@chromium.org>
> > Cr-Commit-Position: refs/heads/main@{#1264086}
>
> Bug: 41491333
> Change-Id: I2a93770ae810aa9b4db78154aa5bdcb7c35ad39e
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5320210
> Owners-Override: Peter Marshall <petermarshall@chromium.org>
> Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
> Reviewed-by: Peter Marshall <petermarshall@chromium.org>
> Commit-Queue: Peter Marshall <petermarshall@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1264407}

Bug: 41491333
Change-Id: I0b6aa2e0d16e18e0f3a070d7bf8b81a6f8c0d45e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5318842
Commit-Queue: Yi Gu <yigu@chromium.org>
Commit-Queue: Christian Biesinger <cbiesinger@chromium.org>
Reviewed-by: Christian Biesinger <cbiesinger@chromium.org>
Auto-Submit: Yi Gu <yigu@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1264727}