Update ApprovalTests nuget package and remove extern alias workaround

[ViktorHofer]

Commit 1: Reapply "Update ApprovalTests to 7.0.0 and revert workaround
Commit 2: Update System.Memory version in test to avoid NuGet downgrade error

The second commit 2 is again a workaround until we can update System.Memory's version to 4.6.3 in the repo.

[adamsitnik]

LGTM, thank you @ViktorHofer !

[SimonCropp]

do u want a pr that moves this to Verify?

[ViktorHofer]

I don't have much context here. Are you saying that ApprovalTests is legacy and Verify is the new thing?

[SimonCropp]

@ViktorHofer from the readme https://github.com/approvals/ApprovalTests.Net

This project is not being actively maintained. Instead consider using Verify. See Migrating from ApprovalTests for more information.

[ViktorHofer]

Ah I see. Yes moving to Verify would be great then.

[SimonCropp]

@ViktorHofer so the current release of Verify.Xunit https://www.nuget.org/packages/Verify.Xunit/ relies on xunit 2.9.3. can we update xunit ?

[ViktorHofer]

Usually this should be fine but this repo uses "Arcade 9" (our own Engineering repo) which references an older xunit version: https://github.com/dotnet/arcade/blob/13b20849f8294593bf150a801cab639397e6c29d/src/Microsoft.DotNet.Arcade.Sdk/tools/DefaultVersions.props#L86

You can bump the version by setting these few properties in Versions.props:

    <XUnitVersion>2.9.3</XUnitVersion>
    <XUnitAnalyzersVersion>1.22.0</XUnitAnalyzersVersion>
    <XUnitRunnerVisualStudioVersion>3.1.1</XUnitRunnerVisualStudioVersion>

Please also update the versions in Directory.Packages.props.