Fix text.Caret batch and blink

[sakkee]

Problem

• If no batch is provided to the text.Caret class, text.Caret won't be added to any batch.
• When deleting the text.Caret, the blink function isn't unscheduled.

Change summary

• In the init function of text.Caret, create the vertex list with self._batch instead of only the parameter batch, as self._batch is the text layout's batch if no batch is provided as a parameter.
• Unschedule the blink function when deleting the Caret.

[benmoran56]

Nice catch! Thank you for the PR.