Add commands to get current selected tests/profiles

[connor4312]

Expose API commands to get the currently selected tests and profiles

• vscode.commands.executeCommand('testing.getSelectedProfiles') -> { controllerId: string, kind: TestrunProfileKind, label: string }[]
• vscode.commands.executeCommand('testing.getExplorerSelection') -> { include: TestItem[], exclude: TestItem[] } (like a TestRunRequest)

[connor4312]

You can test this by modifying the selfhost test provider extension