[Gutenberg] Integrate alpha version v1.69.0-alpha2

[fluiddot]

The purpose of this PR is to integrate the latest changes from Gutenberg Mobile via the alpha version v1.69.0-alpha2, and update the Aztec version of WordPressEditor library to v1.5.3 as it's required by the changes.

Changes:

• Fix text formatting mode lost after backspace is used gutenberg-mobile#4423
• RichText/AztecView - Enable customizing the font size for the Heading and Preformatted block. gutenberg-mobile#4414 (the changes of this PR were merged along the previous one)

Regression Notes

1. Potential unintended areas of impact
   All changes should only affect the editor hence, I don't foresee any other unintended areas of impact.

2. What I did to test those areas of impact (or what existing automated tests I relied on)
   Both PRs have been manually tested.

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

PR submission checklist:

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

[peril-wordpress-mobile]

You can trigger optional UI/connected tests for these changes by visiting CircleCI here.

[geriux]

LGTM! Thanks for working on this 🚀

[peril-wordpress-mobile]

You can test the changes on this Pull Request by downloading the APKs:

• Jetpack-pr-15796-build-118046.apk

• WordPress-pr-15796-build-118046.apk