Contact Form: improve accessibility

[jeherve]

There are different ways we could work on improving the usability and accessibility of the contact form feature. Let's take a closer look at the different issues:

### Tasks
- [ ] #16685
- [ ] #30762
- [ ] #14155
- [ ] https://github.com/Automattic/jetpack/issues/34281
- [ ] https://github.com/Automattic/jetpack/issues/34253
- [ ] https://github.com/Automattic/jetpack/issues/34282
- [ ] https://github.com/Automattic/jetpack/issues/34283
- [ ] https://github.com/Automattic/jetpack/issues/34235
- [ ] https://github.com/Automattic/jetpack/pull/34272
- [ ] https://github.com/Automattic/jetpack/pull/34277
- [ ] https://github.com/Automattic/jetpack/issues/34501
- [ ] https://github.com/Automattic/jetpack/issues/34280
- [ ] https://github.com/Automattic/jetpack/issues/34502
- [ ] https://github.com/Automattic/jetpack/issues/34504
- [ ] https://github.com/Automattic/jetpack/pull/34577

### Lower priority: improvements in the classic editor
- [ ] #31203
- [ ] #25027
- [ ] #12574
- [ ] https://github.com/Automattic/jetpack/issues/34279

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Related discussion: p1698591039559549-slack-C0299DMPG PT: pf5801-87-p2

[chrisbliss18]

Extended the due date because we added some additional tasks.

[github-actions[bot]]

This issue has been marked as stale. This happened because:

• It has been inactive for the past 6 months.
• It hasn’t been labeled `[Pri] BLOCKER`, `[Pri] High`, `[Type] Feature Request`, `[Type] Enhancement`, `[Type] Janitorial`, `Good For Community`, `[Type] Good First Bug`, etc.

No further action is needed. But it's worth checking if this ticket has clear reproduction steps and it is still reproducible. Feel free to close this issue if you think it's not valid anymore — if you do, please add a brief explanation.