fix: shift-tab does not work in FluentPopover, and tab/shift-tab on the popover anchor while popover is open does not close it

[adamint]

🐛 Bug Report

When navigating through a popover with the keyboard, shift + tab should go to the previous element. Instead, it moves to the next element in the popover.

Also, tabbing/shift-tab with the popover open while focus is on the popover anchor does not close the popover, as it should.

Repro by focusing Open Callout 1 and pressing tab/shift-tab -> https://www.fluentui-blazor.net/Popover

(a mix of shift+tab and tab were used in this video, the fact that you cannot tell is the problem!)

Grabacion.2025-09-11.131743.mp4

💻 Repro or Code Sample

💁 Possible Solution

The code in #4093 could be tweaked for the popover component? It handles both of the cases at issue here.

🔦 Context

dotnet/aspire#10129

[adamint]

@vnbaaij when #4093 is merged, I would be happy to contribute a fix myself.

[vnbaaij]

@vnbaaij when #4093 is merged, I would be happy to contribute a fix myself.

I've just approved that PR. Will merge once checks are done