Intoduce KateTextHintManager

Waqar Ahmed requested to merge work/texthintproviders into master

KateTextHintManager provides centralized async interface to show text hints. It uses KTextEditor::TextHintInterface::textHint() to know when a text hint it is requested. It then sends a request to all providers to create text hint and send it back when the text hint is ready. This allows us to show information from multiple sources inside one tooltip and avoids that everyone has to implement a provider and manage it from scratch.

BUG: 467322

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