Fix writingMode support in dynamic blocks

[andrewserong]

Add writingMode to the style engine, to support dynamic blocks. This backports some PHP changes that were missed in previous WP core releases:

• Add Typography: text orientation (writing mode) gutenberg#50822
• Gutenberg Plugin: Add hook to allow writing-mode as a safe CSS property gutenberg#54581

For the issue this resolves, see: WordPress/gutenberg#65910

Trac ticket: https://core.trac.wordpress.org/ticket/62189

This PR adds support for the writing mode (orientation) typography block support for dynamic blocks, such as the Site Title block. Without this change, currently (in WP 6.7 Beta 1 and Beta 2) if you go to update the Site Title block and give it a vertical orientation, it'll look fine within the site editor, but still display as horizontal on the site frontend.

To test this PR, open up the site editor, select the site title block, and switch its text orientation in the block inspector to be vertical. Save the template, and view the site frontend. Here is a quick screenshot to show where to update the text orientation (writing mode):

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[t-hamano]

LGTM! Thanks for the fix 👍

[aaronrobertshaw]

Thanks for cleaning this up @andrewserong 👍

This tests well for me:

I only have a minor question around whether we need a @since comment at all for this one in the docblock.

[andrewserong]

Thanks for the reviews, everyone! 🙇

Committed in r59199.