Onboarding: Add support for RTL site launch stylesheet to ETK

[p-jackson]

Changes proposed in this Pull Request

• Enqueue the RTL stylesheet when is_rtl()

Copying prior art for how this is done in the ETK plugin:

• wp-calypso/apps/editing-toolkit/editing-toolkit-plugin/dotcom-fse/class-full-site-editing.php

  Line 139 in 961a9bd

  $style_file = is_rtl()

• wp-calypso/apps/editing-toolkit/editing-toolkit-plugin/common/index.php

  Line 131 in 961a9bd

  $style_file = is_rtl()

Before
(see how the margins are all strange)

After
(also includes the fix from #47889)

Testing instructions

• yarn dev --sync and sandbox an un-launched site
• Open the launch flow and see that the margins are all looking correct now
• Open the network tab and see that editor-site-launch.rtl.css is being loaded and the non-rtl file isn't

[matticbot]

Test live: https://calypso.live/?branch=add/rtl-support-to-etk-launch

[matticbot]

This PR does not affect the size of JS and CSS bundles shipped to the user's browser.

Generated by performance advisor bot at iscalypsofastyet.com.

[matticbot]

Caution: This PR affects files in the Editing Toolkit Plugin on WordPress.com
Please ensure your changes work on WordPress.com before merging.

D53548-code has been created so you can easily test it on your sandbox. See this FieldGuide page about developing the Editing Toolkit Plugin for more info: PCYsg-ly5-p2

[lsl]

LGTM, do you know why "Select a domain" isn't being translated? The translation exists, I'm thinking maybe a timing issue with the initial render.

[p-jackson]

do you know why "Select a domain" isn't being translated? The translation exists, I'm thinking maybe a timing issue with the initial render.

That's this issue #47884

@lsl But what do you mean about the translation exists? When I look up translate.wordpress.org I don't see it 😕 Have I been looking in the wrong place for ETK strings?

[lsl]

Oh I checked .com, it's a string from 2016, are we getting etk translations from .org?

[p-jackson]

@lsl yes that's my understanding (afaik, I've been working with that assumption and nothing's contradicted it yet). My guess is that makes it easiest to deliver the translations to atomic.