MSTest.Sdk: stop using VersionOverride so CPM with CentralPackageVersionOverrideEnabled=false works

[Copilot]

MSTest.Sdk's .targets set both Version and VersionOverride on every implicit PackageReference. Projects that enable Central Package Management with <CentralPackageVersionOverrideEnabled>false</CentralPackageVersionOverrideEnabled> then fail restore with NU1013 (see discussion #7440, issue #7441).

Changes

• Branch on ManagePackageVersionsCentrally in every SDK .targets (VSTest, Runner/ClassicEngine, Runner/NativeAOT, Features/Aspire, Features/Playwright):
  • When CPM is off: emit Version as conditional nested metadata on the PackageReference.
  • When CPM is on: emit the PackageReference with no version metadata and add a matching PackageVersion item — works regardless of CentralPackageVersionOverrideEnabled.
• Acceptance test: RunTests_With_CentralPackageManagement_Standalone previously didn't actually enable CPM. It now generates a Directory.Packages.props with ManagePackageVersionsCentrally=true and CentralPackageVersionOverrideEnabled=false, exercising the regressing scenario.
• README: design notes rewritten to document the new pattern and explain why VersionOverride is no longer used; also fixed an IsImplictlyDefined → IsImplicitlyDefined typo.

Pattern applied

<PackageReference Include="MSTest.TestFramework" Sdk="MSTest">
  <Version Condition=" '$(ManagePackageVersionsCentrally)' != 'true' ">$(MSTestVersion)</Version>
</PackageReference>
<PackageVersion Include="MSTest.TestFramework" Version="$(MSTestVersion)"
                Condition=" '$(ManagePackageVersionsCentrally)' == 'true' " />

Compatibility note

Users who currently declare a PackageVersion for SDK-managed packages (e.g. MSTest.TestFramework, Microsoft.NET.Test.Sdk) in their own Directory.Packages.props will now get a duplicate-PackageVersion error and should remove those entries — overriding the SDK's defaults is done via the existing MSTestVersion/MicrosoftNETTestSdkVersion/etc. properties.

[Copilot]

Pull request overview

Updates MSTest.Sdk MSBuild targets to stop relying on VersionOverride so Central Package Management (CPM) restores succeed even when CentralPackageVersionOverrideEnabled=false.

Changes:

• Replace VersionOverride-based implicit PackageReference versioning with a CPM-aware pattern: Version metadata when CPM is off, PackageVersion items when CPM is on.
• Fix/strengthen the CPM acceptance test to actually enable CPM and set CentralPackageVersionOverrideEnabled=false.
• Refresh MSTest.Sdk README design notes to document the new approach and correct an attribute name typo.

Show a summary per file

File	Description
test/IntegrationTests/MSTest.Acceptance.IntegrationTests/SdkTests.cs	Updates acceptance test to enable CPM + strict override mode and validate restore/build still succeeds.
src/Package/MSTest.Sdk/Sdk/VSTest/VSTest.targets	Switches implicit package versioning to CPM-aware Version/PackageVersion pattern.
src/Package/MSTest.Sdk/Sdk/Runner/NativeAOT.targets	Applies the CPM-aware versioning pattern to NativeAOT runner dependencies and extensions.
src/Package/MSTest.Sdk/Sdk/Runner/ClassicEngine.targets	Applies the CPM-aware versioning pattern to Classic runner dependencies and extensions.
src/Package/MSTest.Sdk/Sdk/Features/Playwright.targets	Applies the CPM-aware versioning pattern for the Playwright feature package.
src/Package/MSTest.Sdk/Sdk/Features/Aspire.targets	Applies the CPM-aware versioning pattern for the Aspire feature package.
src/Package/MSTest.Sdk/README.md	Documents the new guidance/pattern and removes VersionOverride recommendation.

Copilot's findings

• Files reviewed: 7/7 changed files
• Comments generated: 2

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