Add validations to Monaco

[colin-grant-work]

What it does

Fixes #11241 by removing the buggy ValidatedPreferenceProxy implementation in favor of adding validations for a few key preferences to Monaco's own validation system for editor preferences.

How to test

1. Open a workspace and open a text file in that workspace.
2. In that workspace, set e.g. editor.fontSize to some non-default value.
3. Observe that the new setting takes effect in your open file.
4. In user scope, set the same preference to some other non-default value.
5. Observe that that new setting does not take effect in your open file because it is overridden in a higher-priority scope.

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1. Also confirm that the testing steps for Validate Preferences Used in Editor #10607 and Ensure that old values aren't cached inappropriately #10965 still go as expected.

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

[vince-fugnitto]

I confirmed that the first part of the steps to test is successful, preferences at higher scopes have precedence and apply (ex: workspace over user).

I did notice however that:

• the browser tests fail on CI
• there is no validation message when setting an invalid preference (even with #11025 I understood that it should happen for manual updates by the user)

[colin-grant-work]

• the browser tests fail on CI

I'll check into this.

• there is no validation message when setting an invalid preference (even with #11025 I understood that it should happen for manual updates by the user)

This is expected: Monaco doesn't provide any indication that the user has done something wrong; it just uses a different value. With this code, the PreferenceValidatioService, which issued those warnings, is no longer in use, but I haven't removed it because I think it could be a useful way to provide feedback in the preference UI, with tweaks to provide detailed information. Have to compare it with just using AJV, though.

[msujew]

The changes are looking good to me 👍

• Preferences scopes seem to use the correct precedence now
• Monaco preferences (minimap, rendering whitespace) continues to work correctly
• Setting a preference manually to an invalid value shows a warning and the default value is applied