Simplify Pull Request template (#39229)

* Update PULL_REQUEST_TEMPLATE.md

* Update PULL_REQUEST_TEMPLATE.md

* Add instructions and relevant links to the top.

* Reduce the introductory links to a single one

Link to the Contributing Guidelines

* Extend the contributing guidelines

Extend the contributing guidelines by adding coding standards and accessibility testing.

* Add guideline asking contributors to check React Native files, too

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,30 +1,19 @@
-<!-- Learn the overall process and best practices for pull requests at https://github.com/WordPress/gutenberg/blob/HEAD/docs/contributors/repository-management.md#pull-requests. -->
+<!-- Thanks for contributing to Gutenberg! Please follow the Gutenberg Contributing Guidelines:
+https://github.com/WordPress/gutenberg/blob/trunk/CONTRIBUTING.md -->
 
-<!-- Gutenberg's license is in the process of updating to be dual-licensed under the GPL and MPL. As part of that transition, all new contributions are dual-licensed. For more information, see: https://github.com/WordPress/gutenberg/blob/trunk/LICENSE.md -->
+## What?
+<!-- In a few words, what is the PR actually doing? -->
 
-## Description
-<!-- Please describe what you have changed or added -->
+## Why?
+<!-- Why is this PR necessary? What problem is it solving? Reference any existing previous issue(s) or PR(s), but please add a short summary here, too -->
+
+## How?
+<!-- How is your PR addressing the issue at hand? What are the implementation details? -->
 
 ## Testing Instructions
 <!-- Please include step by step instructions on how to test this PR. -->
 <!-- 1. Open a Post or Page. -->
 <!-- 2. Insert a Heading Block. -->
 <!-- 3. etc. -->
 
-## Screenshots <!-- if applicable -->
-
-## Types of changes
-<!-- What types of changes does your code introduce?  -->
-<!-- Bug fix (non-breaking change which fixes an issue) -->
-<!-- New feature (non-breaking change which adds functionality) -->
-<!-- Breaking change (fix or feature that would cause existing functionality to not work as expected) -->
-
-## Checklist:
-- [ ] My code is tested.
-- [ ] My code follows the WordPress code style. <!-- Check code: `npm run lint`, Guidelines: https://developer.wordpress.org/coding-standards/wordpress-coding-standards/javascript/ -->
-- [ ] My code follows the accessibility standards. <!-- Guidelines: https://developer.wordpress.org/coding-standards/wordpress-coding-standards/accessibility/ -->
-- [ ] I've tested my changes with keyboard and screen readers. <!-- Instructions: https://github.com/WordPress/gutenberg/blob/HEAD/docs/contributors/accessibility-testing.md -->
-- [ ] My code has proper inline documentation. <!-- Guidelines: https://developer.wordpress.org/coding-standards/inline-documentation-standards/javascript/ -->
-- [ ] I've included developer documentation if appropriate. <!-- Handbook: https://developer.wordpress.org/block-editor/ -->
-- [ ] I've updated all React Native files affected by any refactorings/renamings in this PR (please manually search all `*.native.js` files for terms that need renaming or removal). <!-- React Native mobile Gutenberg guidelines: https://github.com/WordPress/gutenberg/blob/HEAD/docs/contributors/code/native-mobile.md -->
-- [ ] I've updated related schemas if appropriate. <!-- Reference: https://github.com/WordPress/gutenberg/tree/trunk/schemas -->
+## Screenshots or screencast <!-- if applicable -->

CONTRIBUTING.md

@@ -18,6 +18,12 @@ To learn all about contributing to the Gutenberg project, see the [Contributor G
 
 -   As with all WordPress projects, we want to ensure a welcoming environment for everyone. With that in mind, all contributors are expected to follow our [Code of Conduct](/CODE_OF_CONDUCT.md).
 
+-   Contributors should review the [overall process and best practices for pull requests](https://github.com/WordPress/gutenberg/blob/trunk/docs/contributors/repository-management.md#pull-requests), adhering to WordPress' [JavaScript coding standards](https://developer.wordpress.org/coding-standards/wordpress-coding-standards/javascript/) and [accessibility coding standards](https://developer.wordpress.org/coding-standards/wordpress-coding-standards/accessibility/).
+
+-   Accessibility should be top of mind and thoroughly tested by following the [accessibility testing instructions](https://github.com/WordPress/gutenberg/blob/HEAD/docs/contributors/accessibility-testing.md).
+
+-   Verify that any changes in your PR that affect function/class/variable names are mirrored in the corresponding `.native.js` versions of the files to avoid introducing breaking changes in the [React Native Mobile Editor](https://github.com/WordPress/gutenberg/tree/trunk/docs/contributors/code/react-native).
+
 -   You maintain copyright over any contribution you make. By submitting a pull request you agree to release that code under [Gutenberg's License](/LICENSE.md).
 
 ## Reporting Security Issues