Test: debug start dropdown

[isidorn]

• win @joaomoreno
• mac @chrmarti
• linux @Tyriar

Complexity: 2

As per #16258 we have restyled the debug start action in the debug viewlet. Have a worskapce with a 'launch.json' and verify:

• debug start action looks nicely styled both in light and dark theme and shows hover feedback
• adding or renaming configurations in launch.json get picked up by the debug start action