Move cursor to end of text when keyboard input gets activated

[Almost-Senseless-Coder]

When keyboard input gets activated, the insertion point for text remains at the last location where the user inserted text, potentially in the middle of the transcript.

It would be far better if the cursor got moved to the end of the transcript and a new line inserted when activating keyboard input.

To do this, we will likely have to convert the current String value of the transcript to a TextFieldValue, since an ordinary String does not support altering the cursor location.

[Almost-Senseless-Coder]

I forgot to mention this issue in the merge commit to automatically close this, so I'll do so now manually.