Resolve "Loss of input text on comments after preview"

What does this MR do?

Fix Firefox not updating v-model with input after clicking Formatting buttons in Issue Notes. Use insertText util, which triggers input event and updates the value of the field

Are there points in the code the reviewer needs to double check?

How to write a test for this?

Why was this MR needed?

Screenshots (if relevant)

before

after

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests added for this feature/bug
• Review
  • Has been reviewed by Frontend
• Conform by the style guides
• Squashed related commits together
• End-to-end tests pass (package-qa manual pipeline job)

What are the relevant issue numbers?

Closes #42880 (closed)