fix(TextArea): adds character counter alert

[jnm2377]

Closes #12071

Changelog

• adds span with role="alert", visually hidden, and only announces on last 10 characters

Testing / Reviewing

• go to TextArea playground
  • set character counter
  • turn on VO
  • type until you reach the limit, you should see the VO announce the last 10 characters
  • if you delete the last 10 characters, VO character count should be updated
  • any number less than the last 10 should not announce anything
• all test should pass
• TextArea should still work as expected

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