[Global Styles] Implement Global Styles endpoint

[chipsnyder]

Fixes wordpress-mobile/gutenberg-mobile#3163
Related PRs

• WordPressKit [Global Styles] Implement Global Styles endpoint WordPressKit-iOS#394
• Gutenberg-Mobile [Global Styles] Adds new Prop for Global Styles Settings gutenberg-mobile#3459
• Gutenberg [RN Mobile][Global Styles] Adds new Prop for Global Styles Settings WordPress/gutenberg#30544

This change is dependent on: WordPress/gutenberg#29969

To test:

You can enable and disable the feature by:

1. Clicking your Avatar from the My Site Screen
2. Navigate to App Settings > Debug
3. Toggle "Global Style Settings" for the desired Setting

Regression Tests:

These should be run on a site with "Global Style Settings" disabled or a site that doesn't have WordPress 5.8 installed:

• Default Colors - Check that default colors still load - steps
• Default Gradients - Check that default gradients still load - steps
• Custom Colors - Check that custom colors load in the editor - steps
• Custom Gradients - Check that custom gradients load in the editor - steps
• Offline Support - steps

Tests:

These should be run on a site with "Global Style Settings" enabled and a site that has WordPress 5.8 installed:

• FSE Colors and Gradients - steps
• Offline Support - steps

Regression Notes

1. Potential unintended areas of impact
   None

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:

• I have completed the Regression Notes.
• I have considered adding unit tests for my changes.
• 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]

	Warnings
⚠️	PR is not assigned to a milestone.
⚠️	PR has more than 500 lines of code changing. Consider splitting into smaller PRs if possible.

Generated by 🚫 dangerJS

[peril-wordpress-mobile]

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

[peril-wordpress-mobile]

You can trigger an installable build for these changes by visiting CircleCI here.

[antonis]

Great work @chipsnyder 👍
I started reviewing this and I've run into an issue with a missing gradient selector. I was able to reproduce this on Android too thus this seems unrelated with this PR.
The code changes LGTM but I've seized testing for now till we find out when this was introduced.

Screenshot

[SiobhyB]

@chipsnyder, @antonis, do you have an idea when the changes to GutenbergViewController will be merged here? I'm looking to set this PR as ready for review, but it's not currently building, which I believe is due to the changes from the merged Gutenberg PRs that this PR is connected to:

Thanks in advance!

[chipsnyder]

Hey @SiobhyB I'll work with @geriux to get this merged today since @antonis is AFK. Sorry about that delay and blocker.

[geriux]

LGTM! Ran some tests to check there are no regressions and is all good! Nice work!