Lazily Create Monaco Models in Resource Preference Providers

[tsmaeder]

For a while now, AbstractResourcePreferenceProvider has used monaco editor models to manage the contents of settings files. This creates a circular dependency, because the editor model waits for preferences to be ready and preferences can't be read before the editor model is created. While this seems to work, I think it would be better if we would apply the following changes:

1. Read the file contents directly from the file initially. Only signal "ready" once the file contents have been read
2. Create a monaco model on demand, that is when opening an editor or when setting a preference programatically. Once we have the model, we can keep it just like now.

Opening an editor will create a model, which will wait for preferences to be ready. I also would setting a preference before the preferences provider is ready to be a programming error to be rejected.

[akosyakov]

We should check though that's proper documents settings are applied on preference save:

theia/packages/preferences/src/browser/abstract-resource-preference-provider.ts

Line 131 in f5433ec

const { insertSpaces, tabSize, defaultEOL } = textModel.getOptions();

Editor preferences are used to configure them for monaco models.

[tsmaeder]

Yes, we would continue using models for all changes to the preferences, be it programmatically or by an editor. A save of an unchanged file should be a no-op, though (IMO).

[tsmaeder]

@colin-grant-work do you think we can close this one now? I don't remember all the contents of your PR anymore. If not, what would be left to do?

[colin-grant-work]

@tsmaeder, if you're happy, I'm happy closing it. Technically, the PR didn't do full lazy loading of the Monaco model but just introduced an additional step in the @postConstruct to read the preferences using the file system - the model is then still created as part of the init() method. It's pretty easy to do full lazy loading on top of that work if you view that as desirable, but to me, getting the load done before ready was the biggest issue, and that's taken care of.