Create the vertical header template part and adjust headings

[carolinan]

Create the vertical header template part, and use it in the templates for the design with the vertical header and right aligned blog. Ensure the design has a single H1 heading.

Description
This PR replaces #285,
and the only reason for this is to avoid the merge conflict so that the changes can be merged right away.

I also added the new hidden-blog-heading pattern as a replacement for the plain text heading.

Previous description:

Regarding Issue #279 - the vertical header was outsourced to a template part and registered in the theme.json.
The pattern for the vertical header was inserted and the title was changed to level 0.

The new template part was inserted at all places where the original vertical header was used.
Also all there is now only one h1 on every template. But for the home template "vertical-header-aligned-home-template.php" I have added a h1 with "Blog" like the original home.html - because the blog posting shouldn't be the h1 and there was no other good option to set the h1.
In the archive it's the archive title, on the single pages and posts its the title and in the search results its the query title.

There shouldn't be visible changes as I tested, except the "Blog" title in the home-template.php

[github-actions]

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[github-actions]

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Co-authored-by: carolinan <poena@git.wordpress.org>

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