[WebUI] Support word suggestions

[caisq]

• Display word suggestions (including word completion and next-word prediction) underneath the main input bar.
• The word suggestions are fetched via HTTP GET requests from the textPrediction() interface method.
• Both word completion and next-word predictions are covered.
• When the InputTextPredictionsComponent is shown, the Expand, Spell and X buttons are moved to the said component.
• Add event logging (new event name: TextPredictionSelection.
• Add logic to modify the text in the main text in ways dependent on whether the suggestions are for word completion or NWP.