Update Global Styles endpoint to support non-experimental paths

[antonis]

This updates the Global styles endpoint to use the non-experimental paths for fetching the block editor settings.

📓 Note that the Jetpack side is still dependent on some backend changes so this PR is still a draft.

WordPress-FluxC-Android PR: wordpress-mobile/WordPress-FluxC-Android#2049

To test:

For each of these cases, it'll be enough to open the editor and validate that the correct color options are available. It would also be useful to test using a network monitoring tool to make sure the correct paths are called. This will help ensure you aren't seeing cached data if you're reusing the same site for testing.

• Self-Hosted Site with WP 5.8 and base Gutenberg version
  • Expect the request to be made with __experimental/wp-block-editor/v1
• Self-Hosted Site with WP 5.8 and Gutenberg version >= 11.1
  • Expect the request to be made with /wp-block-editor/v1
• WPCom or Jetpack connected site with WP 5.8 and base Gutenberg version
  • Expect the request to be made with __experimental/wp-block-editor/v1
• WPCom or Jetpack connected site with WP 5.8 and Gutenberg version >= 11.1
  • Expect the request to be made with /wp-block-editor/v1

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)
   Check WordPress-FluxC-Android PR

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.

[peril-wordpress-mobile]

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

• Jetpack-pr-15002-build-112500.apk
• WordPress-pr-15002-build-112500.apk

[chipsnyder]

🚢 wordpress-mobile/WordPress-FluxC-Android#2049 (review)