Fix broken links in editor documentation

[derekblank]

What?

Fixes a handful of broken links in the Editor documentation.

Why?

To encourage external code contributions, and also not have broken links in documentation.

How?

Finds and replaces the related updated link URL for broken links.

Testing Instructions

Referenced documentation links should not 404.

[github-actions]

Flaky tests detected in aa1c9c3.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/5216025692
📝 Reported issues:

• [Flaky Test] page-list submenu user interactions #51348 in /test/e2e/specs/editor/blocks/navigation.spec.js
• [Flaky Test] should allow to return Global Styles root when example is clicked #50799 in /test/e2e/specs/site-editor/style-book.spec.js
• [Flaky Test] should disappear when closed via click event or Escape key #50807 in /test/e2e/specs/site-editor/style-book.spec.js
• [Flaky Test] should open correct Global Styles panel when example is clicked #50839 in /test/e2e/specs/site-editor/style-book.spec.js

[fluiddot]

LGTM 🎊 !

[t-hamano]

Thanks for the PR, @derekblank.

While reviewing this PR, I found another broken link regarding Appium:

gutenberg/docs/contributors/code/react-native/getting-started-react-native.md

Line 114 in 5a1d376

- [Appium CLI](https://appium.io/docs/en/about-appium/getting-started/) installed and available globally. We also recommend using [appium-doctor](https://github.com/appium/appium-doctor) to ensure all of Appium's dependencies are good to go. You don't have to worry about starting the server yourself, the tests handle starting the server on port 4723, just be sure that the port is free or feel free to change the port number in the test file.

Instead of https://appium.io/docs/en/about-appium/getting-started/, https://github.com/appium/appium/blob/1.x/docs/en/about-appium/getting-started.md may be the currently valid link.

If you would like, how about responding with this PR?

[derekblank]

@t-hamano Thanks for reviewing, and great suggestion! I agree that linking to GitHub would likely be more stable. I've updated the docs. 👍

[t-hamano]

LGTM! Thanks for the update 👍