Prevent language definitions from being read before they are ready

[AndreasArvidsson]

Today we load a language definition whenever the document opens

cursorless/packages/cursorless-engine/src/languages/LanguageDefinitions.ts

Line 86 in 1bffae5

void this.loadLanguage(document.languageId);

The problem is that if they have the scope visualizer running we call the get method before the update is done and we get a error message

cursorless/packages/cursorless-engine/src/languages/LanguageDefinitions.ts

Line 156 in 1bffae5

get(languageId: string): LanguageDefinition | undefined {