Admin bar: Update the Edit Site link

[carolinan]

What?

Partial for #63785
Closes #63784 (based on #63785 (comment))

This PR changes the Edit Site link in the admin bar to point to the top level (the "home") of the Site Editor, instead of opening the current template.

Based on feedback in https://core.trac.wordpress.org/ticket/62368, the Edit Site link also shows in the admin area.
Showing the link while in the admin area makes the admin bar more consistent and makes it easier to use, since you can use your muscle memory.

This PR replaces two stale PR's: #66894 and #63835

How?

By using the filter, the current menu item is replaced, since they share the same id: "site-editor" (There is no need to remove the current menu item first, it is replaced).
The template global and the query args are removed, since they are no longer needed.
The capitalization is changed to Edit Site, to match a change that is already merged in to 6.8: https://core.trac.wordpress.org/ticket/62971

I used 41 as the priority, because it is what was used when the menu item was first added to Gutenberg, in a compat file that has since been deleted. I am not entirely sure what this is based on, but it is probably because themes have priority 40.

Testing Instructions

Activate a block theme.
Confirm that the Edit Site link shows in the admin bar, and that it leads to the Site Editor, without opening a specific template.
Activate a classic theme and confirm that the link does not show.

Screenshots or screencast

This screenshot shows the new link in the admin bar while in the admin area:

[github-actions]

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Co-authored-by: carolinan <[email protected]>
Co-authored-by: shail-mehta <[email protected]>
Co-authored-by: ndiego <[email protected]>
Co-authored-by: richtabor <[email protected]>

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[github-actions]

Flaky tests detected in 9e2d9b1.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/13449892303
📝 Reported issues:

• [Flaky Test] Should insert content using the global inserter #57525 in /test/e2e/specs/widgets/editing-widgets.spec.js

[shail-mehta]

With Block Theme (Active TT5 Theme):

If Classic Theme Active: (TT1 Theme)

[carolinan]

@karmatosed @richtabor @WordPress/gutenberg-design
Hi, the feedback I am looking for regarding this PR is if it is acceptable from your design perspective to show the Edit Site link in the toolbar in the admin area.

Personally I prefer it to show in the admin area, (because I don't have to think). But I believe this is a change where there may be a difference of opinion and I don't want to commit a change that will then be a surprise.