[FedCM[ Show 3.5 accounts on the modal dialog when there are more than 4

The modal dialog in the button flow has more space than the widget flow
does. Per UX suggestion, change the number to 3.5 to increase the
chance of user seeing all their accounts without scrolling.

Bug: 41491333
Change-Id: I858dfa10a41909649648c1ef5773dbe2e40b58bc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5426936


Commit-Queue: Zachary Tan <tanzachary@chromium.org>
Reviewed-by: Zachary Tan <tanzachary@chromium.org>
Commit-Queue: Yi Gu <yigu@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1283132}