SmoothScrollIntoView method should be truly asynchronous

[Vijay-Nirmal]

Describe the bug

Currently SmoothScrollIntoViewWithIndexAsync is not truly asynchronous but it will return a Task.

WindowsCommunityToolkit/Microsoft.Toolkit.Uwp.UI/Extensions/ListViewBase/ListViewExtensions.SmoothScrollIntoView.cs

Lines 29 to 30 in 8ecc496

	/// <returns>Note: Even though this return <see cref="Task"/>, it will not wait until the scrolling completes</returns>
	public static async Task SmoothScrollIntoViewWithIndexAsync(this ListViewBase listViewBase, int index, ScrollItemPlacement itemPlacement = ScrollItemPlacement.Default, bool disableAnimation = false, bool scrollIfVisible = true, int additionalHorizontalOffset = 0, int additionalVerticalOffset = 0)

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

Steps to Reproduce

1. Use SmoothScrollIntoViewWithIndexAsync with animation ON, you will see it won't wait until the animation completes

Expected behavior

SmoothScrollIntoView method should be truly asynchronous. It should wait until the animation completes

Environment

NuGet Package(s): Not Released / Master Branch

Package Version(s): Not Released / Master Branch

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

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

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

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

PR #4129

Hello Vijay-Nirmal, thank you for opening an issue with us!

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