Better error when workload set version uses package version format

[Copilot]

Users occasionally specify a workload set version in the internal NuGet package format (e.g. 10.105.0, 11.100.0-preview.5.26309.3) instead of the user-facing format (10.0.105, 11.0.100-preview.5). Previously this produced a confusing NuGet "package not found" failure; now it produces a clear error with the corrected version.

The user-facing format always has 0 as the minor component — a non-zero minor is the diagnostic signal.

Changes

• WorkloadSetVersion.cs — adds IsWorkloadSetVersionInPackageVersionFormat(string, out string?) which detects the wrong format and computes the corrected version string (8.203.1 → 8.0.203.1, 11.100.0-preview.5.26309.3 → 11.0.100-preview.5.26309.3)
• WorkloadSetVersion.Validation.cs — deleted; was an orphaned file with conflicting duplicate definitions not compiled into any project
• InstallingWorkloadCommand.cs — validates both --version command-line values and workloadVersion from global.json, throwing early with a helpful message
• WorkloadSearchVersionsCommandDefinition.cs — extends the existing version argument validator to emit the specific error instead of a generic "unrecognized argument"
• CliCommandStrings.resx / CommandDefinitionStrings.resx — two new error strings; all XLF files regenerated

Error messages

'10.105.0' is not a valid workload set version. The workload set version should have the form
'major.0.patch' (for example, '10.0.105'). Did you mean '10.0.105'?

'11.100.0-preview.5.26309.3' is not a valid workload set version. ... Did you mean
'11.0.100-preview.5.26309.3'? (Specified in 'path/to/global.json')

[marcpopMSFT]

@copilot Fix the build errors

/mnt/vss/_work/1/s/src/Common/WorkloadSetVersion.cs(70,34): error CS0518: Predefined type 'System.Range' is not defined or imported [/mnt/vss/_work/1/s/src/Resolvers/Microsoft.DotNet.MSBuildSdkResolver/Microsoft.DotNet.MSBuildSdkResolver.csproj]
/mnt/vss/_work/1/s/src/Common/WorkloadSetVersion.cs(70,34): error CS0518: Predefined type 'System.Index' is not defined or imported [/mnt/vss/_work/1/s/src/Resolvers/Microsoft.DotNet.MSBuildSdkResolver/Microsoft.DotNet.MSBuildSdkResolver.csproj]
/mnt/vss/_work/1/s/test/Microsoft.DotNet.Cli.Utils.Tests/TransientSdkResolutionErrorDetectorTests.cs(8,10): error CS0246: The type or namespace name 'FactAttribute' could not be found (are you missing a using directive or an assembly reference?) [/mnt/vss/_work/1/s/test/Microsoft.DotNet.Cli.Utils.Tests/Microsoft.DotNet.Cli.Utils.Tests.csproj]
/mnt/vss/_work/1/s/test/Microsoft.DotNet.Cli.Utils.Tests/TransientSdkResolutionErrorDetectorTests.cs(8,10): error CS0246: The type or namespace name 'Fact' could not be found (are you missing a using directive or an assembly reference?) [/mnt/vss/_work/1/s/test/Microsoft.DotNet.Cli.Utils.Tests/Microsoft.DotNet.Cli.Utils.Tests.csproj]

[Copilot]

@copilot Fix the build errors

/mnt/vss/_work/1/s/src/Common/WorkloadSetVersion.cs(70,34): error CS0518: Predefined type 'System.Range' is not defined or imported [/mnt/vss/_work/1/s/src/Resolver...

Fixed in the latest commit:

1. WorkloadSetVersion.cs — replaced the C# range indexer [sections[0].Length..] with Substring(sections[0].Length) for net472 compatibility (both System.Range and System.Index are unavailable on full framework). Verified the Microsoft.DotNet.MSBuildSdkResolver project now builds cleanly.

2. TransientSdkResolutionErrorDetectorTests.cs — converted from xUnit [Fact] to MSTest [TestClass]/[TestMethod] to match the project's MSTest.Sdk configuration. Verified the Microsoft.DotNet.Cli.Utils.Tests project now builds cleanly.