Revert passing ExcludeRestorePackageImports during restore (#14274)

[ViktorHofer]

Reverts the change from #14274, which injected ExcludeRestorePackageImports=true into the implicit restore global properties (behind change wave 18.10) so that NuGet's restore re-invocation would reuse MSBuild's initial evaluation instead of forcing a second one.

Why revert

The change breaks restore for projects that have a nonexistent <ProjectReference>. Once the top-level restore evaluation shares the same global property set that NuGet's inner _GenerateRestoreProjectPathWalk invocation uses, that walk runs in the same project instance and its unfiltered _RestoreProjectPathItems (which contains the raw ProjectReference paths, including missing ones) leaks into _GenerateRestoreGraph's _GenerateRestoreGraphProjectEntry MSBuild call. That call does not set SkipNonexistentProjects, so it fails with MSB3202 instead of skipping the missing project.

NuGet.targets(571,5): error MSB3202: The project file "...\TestLibrary\TestLibrary.csproj" was not found.

This regressed the dotnet/sdk test ItCanTestAMultiTFMProjectWithImplicitRestore — see dotnet/sdk#55245 for the full root-cause analysis and repro.

Details

• Only the implicit-restore (-restore switch / ExecuteRestore) path was affected; explicit dotnet restore / -t:Restore never added the property.
• Reproduced with dotnet build -t:Restore /p:ExcludeRestorePackageImports=true on a multi-TFM project with a dangling ProjectReference: without the property restore succeeds (missing project skipped gracefully); with it, MSB3202.

What this PR does

• Removes the ExcludeRestorePackageImports=true injection in XMake.ExecuteRestore, replacing it with a comment documenting why the property must not be set there.
• Removes the ExcludeRestorePackageImports / ExcludeRestorePackageImportsValue constants and the two related unit tests.
• Removes the 18.10 ChangeWaves.md bullet for this feature.
• Retains change wave 18.10 itself — it is still used by the -getProperty/-getItem evaluation change (Add opt-in partial (stop-after-pass) project evaluation #14290).

[Copilot]

Pull request overview

Reverts the /restore (and restore-only /t:Restore) behavior introduced in #14274 that injected ExcludeRestorePackageImports=true into restore global properties (behind change wave 18.10), after it was found to break restore in scenarios with a nonexistent <ProjectReference>.

Changes:

• Removed the ExcludeRestorePackageImports=true global-property injection from XMake.ExecuteRestore and replaced it with an explanatory comment documenting the failure mode.
• Deleted the MSBuildConstants.ExcludeRestorePackageImports* constants and removed the unit tests that validated the injected-property behavior.
• Updated ChangeWaves.md to remove the 18.10 bullet that described the reverted feature.

Show a summary per file

File	Description
src/MSBuild/XMake.cs	Stops injecting ExcludeRestorePackageImports during restore; adds rationale comment to prevent reintroduction.
src/MSBuild.UnitTests/XMake_Tests.cs	Removes tests that asserted the (now reverted) injected restore global property behavior.
src/Framework/MSBuildConstants.cs	Removes now-unused ExcludeRestorePackageImports* constants.
documentation/wiki/ChangeWaves.md	Removes the 18.10 changewave bullet describing the reverted restore behavior.

Copilot's findings

• Files reviewed: 4/4 changed files
• Comments generated: 2

[ViktorHofer]

Thanks for the review — addressed both points in 2bf46f00b3:

• Regression test: Added RestoreDoesNotInjectExcludeRestorePackageImports, which asserts restore leaves ExcludeRestorePackageImports empty by default, so the reverted behavior can''t silently reappear. Verified passing on net10.0 and net472.
• ChangeWaves.md typo: Removed the stray arget) on the 18.10 -getProperty/-getItem bullet.