Add property to disable the default set of command-line options for testing

At least for MTP, we need that in microsoft/testfx.

See https://github.com/microsoft/testfx/pull/6140 for context.

Basically, we run official builds with Arcade, but PRs/public builds with `dotnet test`, and we want to unify everything to use `TestingPlatformCommandLineArguments`.

However, for `dotnet test` we will need to add `--results-directory` ourselves to `TestingPlatformCommandLineArguments`, but that then will be picked up by Arcade resulting in duplicate `--results-directory` which is an error.

The ask is to modify (at least) Microsoft.Testing.Platform.targets to conditionally include `--results-directory`, `--report-trx`, `--report-trx-filename`. These will be added by default. Repos that wish to opt-out from that behavior can specify `true`