Describe the bug

A clear and concise description of what the bug is.

When using RangeSelector with narrator, pressing left/right arrow key changes the thumb value, however users are not being updated on the new value of the thumb.

• Is this bug a regression in the toolkit? If so, what toolkit version did you last see it work:

Steps to Reproduce

• Can this be reproduced in the Sample App? (Either in a sample as-is or with new XAML pasted in the editor.) If so, please provide custom XAML or steps to reproduce. If not, let us know why it can't be reproduced (e.g. more complex setup, environment, dependencies, etc...)

Steps to reproduce the behavior:

1. Start Narrator (Ctrl+Win+Enter)
2. Open RangeSelector page
3. Focus one of the RangeSelector thumbs
4. Move thumb with arrow keys, notice that narrator does not announce changes

Expected behavior

A clear and concise description of what you expected to happen.
Narrator should announce changes, ideally also announce upper and lower limit (RangeValuePattern)

Screenshots

If applicable, add screenshots to help explain your problem.

Environment

NuGet Package(s): 

Package Version(s): 

Windows 10 Build Number:
- [ ] Fall Creators Update (16299)
- [ ] April 2018 Update (17134)
- [ ] October 2018 Update (17763)
- [ ] May 2019 Update (18362)
- [ ] May 2020 Update (19041)
- [x] Insider Build (build number: 20236)

App min and target version:
- [ ] Fall Creators Update (16299)
- [ ] April 2018 Update (17134)
- [ ] October 2018 Update (17763)
- [ ] May 2019 Update (18362)
- [ ] May 2020 Update (19041)
- [] Insider Build (xxxxx)

Device form factor:
- [x] Desktop
- [ ] Xbox
- [ ] Surface Hub
- [ ] IoT

Visual Studio 
- [ ] 2017 (version: )
- [ ] 2019 (version: ) 
- [ ] 2019 Preview (version: )

Additional context

Add any other context about the problem here.
The UIA experience of RangeSelector is not ideal, maybe providing the RangeValuePattern for both thumbs improves this. Also more fitting UIA names for the thumbs could be chosen.

Another thing I noticed is that you can move the max-thumb with the minthumb if you keep pressing right-key. Similiarly, focusing the max-thumb and pressing down left-key eventually moves the min-thumb. Moving the thumbs with the mouse does not exhibit that behavior. Is that arrowkey behavior by design?