Standardize custom events, add is* helpers

[TwitchBronBron]

• Standardize the custom events sent from the debug adapter to the client.
• add is* helper functions for each event that abstracts the need to hardcode magic strings in the client.
• restructure the LogOutputEvent and DebugServerLogOutputEvent bodies to be an object so we can more easily expand upon them in the future without breaking backwards compatibility.

NOTE: this is technically a breaking change since the event names and some structures have changed, so the vscode extension will need to be updated at the same to support these changes.

Depends on:

• Better compile error handling roku-deploy#96