[NNotepad] Debounced refresh()

[ibelem]

Thanks @inexorabletash for asking to double check if the content model change callbacks are throttled when deleting $('#input').addEventListener('input', Util.debounce(refresh, 500)); in #257. This was indeed a wrong ignoring.

The shape of the IModelContentChangedEvent emitted via IModel.onDidChangeContent.
https://github.com/microsoft/monaco-editor/blob/main/src/language/typescript/languageFeatures.ts#L209
https://github.com/microsoft/monaco-editor/blob/main/src/language/common/lspLanguageFeatures.ts#L47

Since there are some code usages above for validate method with 500ms in monaco-editor source code, add debounced refresh() back.

The user experience is better than calling refresh() directly when typing quickly, @inexorabletash @anssiko @Honry PTAL

[Honry]

👍

[inexorabletash]

LGTM, thank you!