Validate Preferences Used in Editor

[colin-grant-work]

What it does

Fixes #10599 by adding a service to validate preference values used by Monaco.
Fixes #10678 by modifying the conditions for emitting events and the affects method of PreferenceProxies

It also improves the typing of JSON schemas and fixes some minor issues related to those typings.

How to test

1. start the application with theia as a workspace.
2. open the dev console to view logs.
3. open the settings.json file for the user or workspace scope.
4. add "editor.tabSize": 2 if it doesn't already exist - the application should work fine.
5. update the value to "editor.tabSize": "true".
6. Observe that application continues working normally as though the preference were set to its default value. There should also be a warning in the console describing the problem and explaining what value is being used.

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[colin-grant-work]

@vince-fugnitto, would you mind taking a look at this? If desired, I can remove the changes related to JSON schema typing - it was convenient when writing the validation, but I think the only actual problems it detected were in the plugin task system, where we were using the taskType (e.g. 'npm') as the schema type, rather than 'object'.

[vince-fugnitto]

I confirmed that the changes address the problem where invalid preferences values would break the app. The framework is now robust where we validate preferences, and fallback properly when incorrect 👍 I really like the tests as well! :)

[vince-fugnitto]

I confirmed that #10599 is resolved with the latest changes 👍

[vince-fugnitto]

The changes work well for me 👍

I confirmed that the preferences are now correctly validated (for example in the case they are manually edited), and if a type or value is invalid the preference will default back to it's default value.

I also confirmed that my previous observation of the multiple logs has been fixed and only one validation message is displayed in the console. The marker in the editor is also present.