Deprecation notices: add details about file/function removals

[jeherve]

Changes proposed in this Pull Request:

In #16433, we determined that we would remove deprecated files and functions 6 months after they've been deprecated.

Let's communicate this to site owners as well, by outputting additional details in the error logs when a deprecation notice is issued.

Jetpack product discussion

• N/A

Does this pull request change what data or activity we track or use?

• N/A

Testing instructions:

• Add the following into a plugin on your site:

function jeherve_test_deprecated_things() {
	require_once JETPACK__PLUGIN_DIR . 'modules/minileven.php';
	$deprecated_function = jetpack_check_mobile();
}
add_action( 'init', 'jeherve_test_deprecated_things' );

• Load your site
• Check your error log: you should see the following:

[09-Jul-2020 08:19:37 UTC] The minileven.php file will be removed from the Jetpack plugin in version 8.9.
[09-Jul-2020 08:19:37 UTC] PHP Deprecated:  minileven.php is <strong>deprecated</strong> since version jetpack-8.3.0 with no alternative available. in /var/www/html/wp-includes/functions.php on line 4913
[09-Jul-2020 08:19:37 UTC] The jetpack_check_mobile function will be removed from the Jetpack plugin in version 8.9.
[09-Jul-2020 08:19:37 UTC] PHP Deprecated:  jetpack_check_mobile is <strong>deprecated</strong> since version jetpack-8.3.0! Use jetpack_is_mobile instead. in /var/www/html/wp-includes/functions.php on line 4713

Proposed changelog entry for your changes:

• Deprecation Notices: provide more information about deprecated files and functions.

[matticbot]

Caution: This PR has changes that must be merged to WordPress.com
Hello jeherve! These changes need to be synced to WordPress.com - If you 're an a11n, please commandeer, review, and approve D46163-code before merging this PR. Thank you!
This revision will be updated with each commit to this PR

[jetpackbot]

Thank you for the great PR description!

When this PR is ready for review, please apply the [Status] Needs Review label. If you are an a11n, please have someone from your team review the code if possible. The Jetpack team will also review this PR and merge it to be included in the next Jetpack release.

E2E results is available here (for debugging purposes): https://jetpack-e2e-dashboard.herokuapp.com/pr-16444

Scheduled Jetpack release: August 4, 2020.
Scheduled code freeze: July 28, 2020

Generated by 🚫 dangerJS against 51fa1b1

[kraftbj]

I really like this. Some questions and a couple of suggestions.

[jeherve]

Thanks for the feedback. I believe I've addressed everything, it should be ready for another round.

[jeherve]

r210265-wpcom