Show both selection and semantic occurrences in the scrollbar

<!-- ⚠️⚠️ 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 scrollbar can only show markers for either semantic or selection-based occurrences of other text in the document. This depends on whether semantic occurrences are available for a document type or not. Semantic occurrences always have priority and disable the selection-based highlighting. This applies only to the scrollbar, all highlighting already exists in the editor itself. There are two closed issues about this: #16042 (scrollbar) and #101552 (minimap). They were closed as "as designed". This issue is about changing that design. The semantic occurrences are marked with a grey dot in the scrollbar. I've set up the colours in the editor to match those of Visual Studio, that is a warm grey. The selection highlighting would also be marked with a grey dot in the scrollbar. I've set up the colours in the editor to match those of Notepad++ (and also [my similar extension for Visual Studio](https://marketplace.visualstudio.com/items?itemName=ygoe.SelectionTodoHighlighter) that already does the scrollbar highlighting), that is a light green. It would be great to use both types of highlighting in the scrollbar. Each with their own colour to match that in the editor. Both colours need their own settings key to adjust them and tell the markers apart. Because semantic highlighting often fails or cannot work at all. In plain JavaScript files, many symbols are unknown and cannot be understood by the editor alone. And when looking for text that isn't even a symbol, like strings or comments, semantic highlighting can never work anywhere. This is when selection highlighting comes in. It's not an either-or, it's a both. One must not suppress the other, even less so when the suppressing one itself has nothing to say w…