Fix: Makes edit mode selector persistent in top toolbar mode.

[vipul0425]

What?

Fixes: #65508

Why?

Edit mode selector was not persistent when we switch to Top toolbar mode in site editor.

How?

This PR makes that button persistent even after toggling to Top toolbar mode.

Testing Instructions

1. Open the site editor
2. Click the pointer icon at the top left and toggle to the edit mode
3. In the settings at the top right of the editor, switch to the top toolbar mode
4. Notice that you can switch editing modes at the top left

Screenshots or screencast

Screen.Recording.2024-09-20.at.12.05.40.PM.mov

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Co-authored-by: vipul0425 <vipulgupta003@git.wordpress.org>
Co-authored-by: youknowriad <youknowriad@git.wordpress.org>
Co-authored-by: jameskoster <jameskoster@git.wordpress.org>
Co-authored-by: andrewserong <andrewserong@git.wordpress.org>

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[youknowriad]

I'm guessing the original thinking is that we wanted to gain space in top toolbar mode to leave enough place for the block toolbar. I think this PR is fine personally. So just want to confirm that it's ok for designers too.

[jameskoster]

It seems necessary to me. I don't see a good reason that activating Top toolbar should prohibit you from switching modes.