Fallback to sending fake key events when receiving input from input-method-v1 and there is no text-input context

When we have no text-input instance, we have no way of communicating more extensive input method events. To still give some input to the client, we fall back to sending fake key events in this case. The key events are synthesised based on the text string that the input method sends, which may result in things that do not actually correspond to real keys. Unfortunately I do not see a way around that. It also has limitations as to what sort of text is supported.

Depends on !2312 (merged) for the qtKeyToXkbKeyCodes function.