[css] Allow extensions to choose to use whether to use CSS default data provider

The CSS language service has had the parameter of whether to use the default data provider (useDefaultDataProvider) for long while now and more recently the exposing of css.customData for extensions which is lovely. However the bundled css-language-features extension sets data providers with useDefaultDataProvider forced to true.

Considering these go together in setting data providers, it would be fantastic to expose useDefaultDataProvider in the same way. This would make it very simple for extensions to support languages/frameworks that deviate from spec. Seems like it would be simple to do as well.