Auto-promote scalar JSON values for arg-bearing CLI options (fixes #8830)

[Evangelink]

Resolves #8830.

Problem

In testconfig.json, a bare scalar like

{ "platformOptions": { "commandLineOptions": { "results-directory": "TestResults" } } }

was read by JsonConfigurationProvider as a presence marker via bool.TryParse for any option whose schema requires an argument. For an arg-bearing option, "timeout": "true" therefore enabled the option with zero args instead of passing "true" as the first argument value — a quiet foot-gun.

Fix

Normalize _singleValueData once at startup using the registered option registry: when an option has Arity.Min >= 1, rewrite the bare scalar key

commandLineOptions:<name>

into the indexed form

commandLineOptions:<name>:0

so the value is consistently surfaced as the first argument by both EnumerateCommandLineOptions and TryGetCommandLineOptionFromProviders.

Optional-arg options (Min=0, Max>=1) remain ambiguous by design and are left untouched (workaround: use the array form ["true"]). Zero-arity and unknown options are also left as-is — the existing validator catches unknown options.

Wire-up

TestHostBuilder.CommonServices.cs builds an OrdinalIgnoreCase option lookup from the system + extension command-line providers and calls the new AggregatedConfiguration.NormalizeJsonCommandLineOptionScalars before EnumerateJsonCommandLineOptions, so the validator and any other consumer sees the rewritten form.

Tests

Added 9 new [TestMethod]s in JsonCommandLineOptionsTests.cs covering:

• arg-bearing scalar promoted
• "true" / "false" strings on arg-bearing options promoted (regression for the original ambiguity)
• non-bool scalar promoted
• zero-arity option left as presence marker
• optional-arg option left untouched (still ambiguous, documented workaround)
• unknown option untouched
• already-indexed JSON untouched
• case-insensitive option lookup
• no-op when no JSON source is registered

All 380 existing Configuration / CommandLine tests pass; full net9.0 build clean with -warnaserror.

[Copilot]

Pull request overview

This PR fixes a long-standing ambiguity in testconfig.json parsing where scalar JSON values for arg-bearing CLI options (e.g., "timeout": "true") could be misinterpreted as a presence marker instead of being treated as the first argument. It does so by normalizing JSON scalar entries into the canonical indexed configuration shape (commandLineOptions:<name>:0) once the option registry is available.

Changes:

• Added JSON-scalar normalization logic in JsonConfigurationProvider and surfaced it via AggregatedConfiguration.NormalizeJsonCommandLineOptionScalars.
• Wired normalization into TestHostBuilder so it runs before JSON options are enumerated/validated.
• Added unit tests covering scalar promotion behavior, case-insensitive lookup, and no-op behavior when no JSON provider is present.

Show a summary per file

File	Description
test/UnitTests/Microsoft.Testing.Platform.UnitTests/Configuration/JsonCommandLineOptionsTests.cs	Adds coverage for scalar-to-indexed normalization across arity and casing scenarios.
src/Platform/Microsoft.Testing.Platform/Hosts/TestHostBuilder.CommonServices.cs	Builds an option-name lookup and invokes JSON normalization before enumerating JSON CLI options.
src/Platform/Microsoft.Testing.Platform/Configurations/JsonConfigurationProvider.cs	Implements the scalar key rewrite (commandLineOptions:<name> → ...:<name>:0) for Arity.Min >= 1.
src/Platform/Microsoft.Testing.Platform/Configurations/AggregatedConfiguration.cs	Exposes a single entry point to normalize JSON command-line scalar entries when a JSON provider is present.

Copilot's findings

• Files reviewed: 4/4 changed files
• Comments generated: 1

[Copilot]

Copilot's findings

• Files reviewed: 4/4 changed files
• Comments generated: 0 new