Restore Site Title's Level toolbar and remove obsolete code

[david-szabo97]

Description

By mistake, we had two edit files. One at /edit.js and one at /edit/index.js. Looks like the Level toolbar functionality was added by this commit 988ba5d#diff-655f76535495d8ae1d82693b57a4ffba at/edit/index.js and later on /edit.js was created again by this commit 0446ed1#diff-655f76535495d8ae1d82693b57a4ffba . After this commit, we lost the Level Toolbar which was residing in the /edit/index.js. Since we had an edit folder and an edit.js file, the import was confusing since we had no idea whether the file or the folder being resolved.

This PR cleans up the mistake by removing the /edit.js and re-adding the Level toolbar.

Note:
We have a component at packages/block-library/src/heading/heading-level-dropdown.js which seems to be very similar to the one used by Site Title. Probably we should extract the component from the Heading block and reuse it here.

How has this been tested?

1. Open Site Editor
2. Add Site Title block
3. Select for editing
4. Shows a control for the heading level

Screenshots

Types of changes

New feature

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.
• I've updated all React Native files affected by any refactorings/renamings in this PR.

[ockham]

Thanks for digging!

It seems like the point of commit 0446ed1#diff-655f76535495d8ae1d82693b57a4ffba (PE #18361) that accidentally recreated /edit.js was to use the newly created Editable component (rather than RichText) to implement the SiteTitle block. This was subsequently changed in #21076 to use the PlainText component instead, and finally, in #22843, it was changed to use the RichText component again.

cc/ @ellatrix who made the Editable and PlainText changes, and @apeatling and @Addison-Stavlo who collaborated on #22843.

Also cc/ @epiqueras who originally added the Level toolbar in 988ba5d#diff-655f76535495d8ae1d82693b57a4ffba (#20361).

Edit: Specifically, I'm curious if we should change the block back to PlainText, since we don't want to offer rich-text editing for blocks like this anyway (instead, we only want to offer formatting that applies to the entire string regardless).

[ockham]

We don't enforce Yoda conditions in our JS (since we're enforcing typed comparisons -- === instead of == -- anyway).

[david-szabo97]

Actually I copy-pasted it from the previous source and yeah, it felt strange to have Yoda conditions in JS. I'll revert this change since I don't like it either.

[ockham]

Note:
We have a component at packages/block-library/src/heading/heading-level-dropdown.js which seems to be very similar to the one used by Site Title. Probably we should extract the component from the Heading block and reuse it here.

That sounds like a great idea for a follow-up PR 👍

[ockham]

Thanks a lot! 🚢