fix: convert toolbar format strings to sentence case

[naurakrbna]

Purpose / Description

Convert toolbar format strings to sentence case to follow Material Design 3 guidelines and maintain consistency with other strings in the app.

Strings changed:

• Format as Bold → Format as bold
• Format as Italic → Format as italic
• Format as Underline → Format as underline
• Insert Horizontal Line → Insert horizontal line
• Insert Heading → Insert heading
• Change Font Size → Change font size
• Insert MathJax Equation → Insert MathJax equation

Fixes

Fixes #15760

[welcome]

First PR! 🚀 We sincerely appreciate that you have taken the time to propose a change to AnkiDroid! Please have patience with us as we are all volunteers - we will get to this as soon as possible.

[github-actions]

Important

Maintainers: This PR contains Strings changes

1. Sync Translations before merging this PR and wait for the action to complete
2. Review and merge the auto-generated PR in order to sync all user-submitted translations
3. Sync Translations again and merge the PR so the huge automated string changes caused by merging this PR are by themselves and easy to review

[david-allison]

Cheers!

Already handled in 518d00c