Formatting Toolbar Popup: Change label from `Title` to `Heading`

1. Please change Heading popup from Title to Heading for consistency.

What do you think?

Thank you

Linux Mint 21.2 Cinnamon
Jami Version: 202307311645

added SprintTo review label

mentioned in commit d62c2ff9

Should id: titleAction be changed to id: headingAction?

Please see comment at https://review.jami.net/c/jami-client-qt/+/25475

Thank you

removed SprintTo review label

added UI/UX label

closed