Deprication of DebugAdapterExecutableCommand

> Please note: With the finalization of this API, we are deprecating the old (proposed) API DebugConfigurationProvider.debugAdapterExecutable and the very old command-based approach (contribution point Debuggers, attribute: adapterExecutableCommand). Please move off those APIs as we plan to remove support for them in the next release.
See https://code.visualstudio.com/updates/v1_30#_debugging-api

This results in the following code being deprecated https://github.com/OmniSharp/omnisharp-vscode/blob/ad8fea90b445f439adf0e9bf179253b9aeceea63/src/features/commands.ts#L50

We will need to update and use [DebugAdapterDescriptorFactory ](https://github.com/Microsoft/vscode/blob/a152a5c7818a13666a5879b4450eb26a4d45fbde/src/vs/vscode.d.ts#L8471)