search query input: Show loading indicator for suggestions

Created by: fkling

Monaco shows "Loading..." in the suggestions box while data is being loaded, which makes it clearer to the user that something is happening.

The solution to this problem might be part of #33007 but I wanted to create a separate issue to track this as a regression.

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While it is possible to get information about the current "suggestions state", show a specific indicator might not be as simple. We should discuss first whether we need an indicator at all.