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

<!-- ⚠️⚠️ Do Not Delete This! feature_request_template ⚠️⚠️ --> <!-- Please read our Rules of Conduct: https://opensource.microsoft.com/codeofconduct/ --> <!-- Please search existing issues to avoid creating duplicates. --> <!-- Describe the feature you'd like. --> The CSS language service has had the parameter of whether to use the default data provider ([`useDefaultDataProvider`](https://github.dev/microsoft/vscode-css-languageservice/blob/c29c007451cd10d3c565250efd8aba44c54b2485/src/languageFacts/dataManager.ts#L36-L37)) for long while now and more recently [the exposing of `css.customData` for extensions](https://github.com/microsoft/vscode/issues/135459) which is lovely. However the bundled `css-language-features` extension [sets data providers with `useDefaultDataProvider` forced to `true`](https://github.dev/microsoft/vscode/blob/c64daad0ff2e7b5fd5e423e54af8a1da7aa2d712/extensions/css-language-features/server/src/cssServer.ts#L204). 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.