Microsoft-ui-xaml: Tab strip scroll bumpers don't disable when scrolling to the edge

Tab strip scroll bumpers don't disable when scrolling to the edge

Steps to reproduce the bug

Steps to reproduce the behavior:

1. Add enough tabs to make the tab strip scrollable, so that the scroll arrows appear.
2. Scroll as much as possible in one direction (left or right)

Expected behavior

The corresponding arrow should be disabled and grayed out to indicate the state of being at the complete left/right. Example with Microsoft Edge (Legacy) tab strip :

Screenshot above on MS Edge, after doing the repro steps, with the _mouse cursor on the arrow button_
As you can see, MS Edge reacts to the edges of the tab strip. (..Mandatory pun)

Actual behavior

Notice that even though you can't scroll anymore, the scroll arrow doesn't reflect this state. (Not grayed out, and reacts to clicks, even though nothing happens

Screenshot above on Windows Terminal, after doing the repro steps, with the _mouse cursor on the arrow button_

Version Info
WinUI 2.4 & WinUI 3alpha, both through their respective branches of Xaml-Controls-Gallery
So that's
NuGet package version:
Microsoft.UI.Xaml 3.0.0-alpha.200210.0
Microsoft.UI.Xaml 2.4.0-prerelease.200203002

| Windows 10 version | Saw the problem? |
| :--------------------------------- | :-------------------- |
| Insider Build (19577) | Yes |
| November 2019 Update (18363) | |
| May 2019 Update (18362) | |
| October 2018 Update (17763) | |
| April 2018 Update (17134) | |
| Fall Creators Update (16299) | |
| Creators Update (15063) | |

| Device form factor | Saw the problem? |
| :-------------------- | :------------------- |
| Desktop | Yes/No |
| Mobile | |
| Xbox | |
| Surface Hub | |
| IoT | |

Additional context

Initially noticed on Windows Terminal and filled it there https://github.com/microsoft/terminal/issues/5053