Monaco editor’s provideCompletionItems callback not firing (TriggerCharacters not working)

I ran into a bug where the monaco editor was not showing the autocomplete dropdown even though I had specified my trigger characters correctly.

The root cause was because of 2 issues:

1. I did not register my custom language using monaco.languages.register(….).
2. Once I did register my language, I was registering it after the editor was already mounted. It must be registered first.