Jetpack: lossless image optimization, part 3

[danluu]

This is a continuation of #38398 and #38573, which has been split into multiple parts to avoid hitting the wpcom size limit, which happened on Automattic/themes#7671. Please see #38398 for more details and context.

As a rough estimate for size of files touch that go into wpcom, we have

% git diff --name-only | grep -v "w.org-assets" | xargs du -ch  
5.8M    total 

#38573 had some instructions for getting a better estimate on wpcom sizes. I can try that and add a comment about that in a bit.

Proposed changes:

• This PR does lossless image optimization on the images not already optimized in Jetpack: lossless image optimization of PNGs in projects/plugins/jetpack #38398 and Lossless image optimization, part 2 #38573, so this should be the final PR in this series. There's room for improvement in other ways, even when it comes to images, but those would be different kinds of optimizations.

Other information:

• Have you written new tests for your changes, if applicable?
• Have you checked the E2E test CI results, and verified that your changes do not break them?
• Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)?

Jetpack product discussion

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

Testing instructions:

• Can test via imagemagick compare or by eyeballing the images to check that they don't appear to have visually changed.

[github-actions]

Are you an Automattician? Please test your changes on all WordPress.com environments to help mitigate accidental explosions.

• To test on WoA, go to the Plugins menu on a WordPress.com Simple site. Click on the "Upload" button and follow the upgrade flow to be able to upload, install, and activate the Jetpack Beta plugin. Once the plugin is active, go to Jetpack > Jetpack Beta, select your plugin, and enable the try/lossless-image-optmization-part-3 branch.

  • For jetpack-mu-wpcom changes, also add define( 'JETPACK_MU_WPCOM_LOAD_VIA_BETA_PLUGIN', true ); to your wp-config.php file.

• To test on Simple, run the following command on your sandbox:

  bin/jetpack-downloader test jetpack try/lossless-image-optmization-part-3
  

  bin/jetpack-downloader test jetpack-mu-wpcom-plugin try/lossless-image-optmization-part-3
  

Interested in more tips and information?

• In your local development environment, use the jetpack rsync command to sync your changes to a WoA dev blog.
• Read more about our development workflow here: PCYsg-eg0-p2
• Figure out when your changes will be shipped to customers here: PCYsg-eg5-p2