i18n extractor: extract strings from Gutenberg Blocks.

[jeherve]

Changes proposed in this Pull Request:

This changes the gulp languages:extract task so it can get the strings from any .js files in the _inc/blocks directory. This is currently where we place the Gutenberg Block files generated by the SDK.

In addition, the task now searches for _n(), _x() and _nx(), so we can account for any @wordpress/i18n localization function.

Testing instructions:

• Checkout the following Calypso branch: remove/gutenberg-jetpack-textdomain - (Calypso PR)
• Run the following command while in the Calypso root dir:

NODE_ENV=production npm run sdk gutenberg client/gutenberg/extensions/presets/jetpack -- \
--output-dir=/DIR_TO_JETPACK/_inc/blocks \
--watch

where DIR_TO_JETPACK is the directory to your local Jetpack repo.

• Switch to this branch in Jetpack.
• Make sure you have gulp globally installed.
• Run gulp languages:extract
• Verify _inc/jetpack-strings.php contains new strings, coming from any of the .js block files (towards the end of the file).
• Start a post.
• Insert some of our Jetpack blocks, verify they're properly translated.
  • To test this, change the Markdown block title to "Settings" and re-run the above Calypso command. "Settings" is a valid string that's already used by Jetpack and it's translated in many of the locales.

Proposed changelog entry for your changes:

• None.

[jeherve]

Currently this does not quite work. The strings generated in the _inc/jetpack-strings.php all have the following format:

_n( "Link to", "jetpack", 1, "jetpack" ), // _inc/blocks/editor.js:25

[jetpackbot]

	Warnings
⚠️	The PR is missing at least one [Status] label. Suggestions: [Status] In Progress, [Status] Needs Review

This is automated check which relies on PULL_REQUEST_TEMPLATE.We encourage you to follow that template as it helps Jetpack maintainers do their job. If you think 'Testing instructions' or 'Proposed changelog entry' are not needed for your PR - please explain why you think so. Thanks for cooperation 🤖

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[tyxla]

This is now ready for review.

[jeherve]

It seems to work well in my tests! 🎉

[kraftbj]

@jeherve I'll ping in Slack. I'm seeing errors when trying to run through your testing steps, so want to confirm if it is me or the PR. Let's hold on to make sure it is just me.

[kraftbj]

I had some issues with Calypso due to stale node_modules and in the course of figuring that out, I upgraded node to 11.0.0. The gulp function didn't work as expected under Node 11, but a downgrade to 10.11.0 + rebuild node-sass resolved that.

Once I got the environment working, tests as expected. 🚢

[tyxla]

Folks, this needs another review because we fixed something we missed: Automattic/wp-calypso#28088 (comment)

Note that I've rebased this branch, so you might want to pull the latest rebased version.

[jeherve]

It seems to work well in my test. Nice work!

[tyxla]

Thanks for landing this one, folks!

Note that the Calypso PR still needs to land before we're able to index translations from blocks: Automattic/wp-calypso#28088