For #109277

- Add more explicit two phase structure to api
- Make opener pass along label when registered

This workbench service handles opening external uris. Unlike the core OpenerService, it also has logic for configuring a default opener and prompting if multiple openers are availble for a given uri

This changes makes a few changes to the openers:

- Move the opener prompting from the extension host into the main thread
- Make the external opener process two phases: get openers and then open. This would let us skip the trusted domain validation for extension handled links if we want to in the future
- Add lifecycle to commands used by the uri opener

For #109277

This change moves the extension uri opener contribution point to instead use the internal `IExternalOpener` api instead of the more generic `IOpener` api. This is required since external uri openers should see the resolved uri that has gone through port forwarding, not the raw uri that the user clicked on

For #109277