Block library: Refactor Quote block to use class names for text align

[gziolo]

Description

Related: #16027, #15751, #16777.

This PR follows-up #16035.

Before:

<!-- wp:core/quote {"align":"right"} -->
<blockquote style="text-align:right" class="wp-block-quote">
	<p>Testing deprecated quote block...</p>
	<cite>...with a caption</cite>
</blockquote>
<!-- /wp:core/quote -->

After:

<!-- wp:quote {"align":"right"} -->
<blockquote class="wp-block-quote has-text-align-right"><p>Testing deprecated quote block...</p><cite>...with a caption</cite></blockquote>
<!-- /wp:quote -->

How has this been tested?

Using one of the existing branches (master probably) add a few Quote blocks and set different text alignments and save your post. Open the same post with this branch and ensure that it still works

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.

[draganescu]

With this change on there is a small inconsistency with master, not sure if intended or not, when text is aligned centre the left border still shows, while on master it doesn't:

This change:

Master:

[gziolo]

With this change on there is a small inconsistency with master, not sure if intended or not, when text is aligned centre the left border still shows, while on master it doesn't:

I partially fixed with 71d2c7f.

This blue thing comes from Twenty Nineteen theme:

I marked this PR as Needs Dev Note as we will need to let theme developers know about this change which needs to happen to make blocks which text alignments easier to style. At the moment they use the very awkward syntax as you can see in 71d2c7f.

[kjellr]

This blue thing comes from Twenty Nineteen theme:
...
I marked this PR as Needs Dev Note as we will need to let theme developers know about this change which needs to happen to make blocks which text alignments easier to style. At the moment they use the very awkward syntax as you can see in 71d2c7f.

I'll get a patch ready for Twenty Nineteen to be compatible with this change. 👍

[kjellr]

Actually, I'm not seeing that blue line issue. 🤔 I don't think the latest version of Twenty Nineteen actually does provide the style you noted above. It provides a border-width and a border-color, but not a position, and then piggybacks off the default styles provided from Gutenberg.

https://themes.trac.wordpress.org/browser/twentynineteen/1.4/style-editor.scss#L393

... and here's how that looks in the editor when I try it out:

[youknowriad]

LGTM 👍