In-App Updates: Add Version model

[momo-ozawa]

Fixes https://github.com/wordpress-mobile/WordPress-iOS/pull/23195#pullrequestreview-2057967801

Description

• Adds the Version model, which has more robust comparison logic

How to test

• Make sure AppUpdateCoordinatorTests is all green

Regression Notes

1. Potential unintended areas of impact n/a

2. What I did to test those areas of impact (or what existing automated tests I relied on) n/a

3. What automated tests I added (or what prevented me from doing so) n/a

PR submission checklist:

• [x] I have completed the Regression Notes.
• [x] I have considered adding unit tests for my changes.
• [x] I have considered adding accessibility improvements for my changes.
• [x] I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

Testing checklist:

• [ ] WordPress.com sites and self-hosted Jetpack sites.
• [ ] Portrait and landscape orientations.
• [ ] Light and dark modes.
• [ ] Fonts: Larger, smaller and bold text.
• [ ] High contrast.
• [ ] VoiceOver.
• [ ] Languages with large words or with letters/accents not frequently used in English.
• [ ] Right-to-left languages. (Even if translation isn’t complete, formatting should still respect the right-to-left layout)
• [ ] iPhone and iPad.
• [ ] Multi-tasking: Split view and Slide over. (iPad)