While `SemanticIndexManager.inProgressPrepareForEditorTask` is not `nil`, show a work done progress in the editor that the current file is being prepared for editor functionality.
I decided to use the indexing progress indicator for this for now because I think it’s too spammy if SourceKit-LSP has two different progress indicators for preparation and indexing. I’ll need to see how this feels like in practice.
rdar://128722609
ecacd7ba2c