[Feature]: Microsoft.Testing.Platform (MTP) support in Test Explorer

Problem / motivation

The Test Explorer is VSTest end-to-end (dotnet test --list-tests, dotnet vstest --ListFullyQualifiedTests, dotnet test --filter … --logger trx, TRX parsing). MTP-only projects get only the degraded DisplayName fallback (TEST-EXPLORER-SPEC.md mentions MTP once), and runs fail.

This is becoming the common case: on .NET 10 SDK, MTP v2 removed the VSTest target shim, and xunit.v3 4.0.0 defaults to MTP v2. Concretely broken against an MTP-only project:

• Discovery pass 1 (dotnet test --list-tests --nologo) — --nologo is rejected in MTP mode (exit code 5, zero tests; verified locally).
• Discovery pass 2 (dotnet vstest <assembly>) — cannot load an MTP-only assembly.
• Execution (--filter FullyQualifiedName=, --logger trx) — these don't exist in MTP mode (MTP uses --filter-class etc. / --report-trx).

Repro: .NET 10 SDK, xUnit v3 project (xunit.v3 4.0.0, <UseMicrosoftTestingPlatformRunner>true</UseMicrosoftTestingPlatformRunner>), global.json with {"test": {"runner": "Microsoft.Testing.Platform"}}, open in VS Code with SharpLsp.

Proposed solution

Detect MTP projects (Microsoft.Testing.Platform reference or test.runner: Microsoft.Testing.Platform in global.json) and switch them to an MTP path: MTP-mode dotnet test --list-tests for discovery, framework filter options for runs, TRX-report extension (or MTP result protocol) for outcomes. Happy to provide a sample repo or test a preview build.

Language relevance

Both C# and F#

Alternatives considered

Running tests via CLI outside the Testing view (works, but loses the explorer); Visual Studio / Rider / C# Dev Kit already run MTP projects in their Test Explorers.

Start with TEST-EXPLORER-SPEC.md and locate the existing VSTest discovery, execution, filtering, and TRX parsing paths. Reproduce the failures with the listed dotnet test and dotnet vstest commands; done means MTP-only projects are detected, discovered, run with the appropriate filters, and their outcomes appear in Test Explorer.