fix: make draggable regions work when devtools is opened on macOS

[zcbenz]

Description of Change

Close #3647.

On macOS the draggable regions would stop working when devtools is opened, because the docked devtools is implemented by placing the devtools view under the main WebContents, and the devtools view itself is not draggable.

This PR makes the devtools view itself draggable to make the draggable regions work, and then put a view above the devtools area to exclude it from dragging.

The UI structure looks like this:

Checklist

• PR description included and stakeholders cc'd
• npm test passes
• tests are changed or added
• relevant documentation is changed or added
• PR release notes describe the change in a way relevant to app developers, and are capitalized, punctuated, and past tense.

Release Notes

Notes: Fix draggable regions stops working when devtools is opened on macOS

[release-clerk]

Release Notes Persisted

Fix draggable regions stops working when devtools is opened on macOS

[trop]

I was unable to backport this PR to "9-x-y" cleanly;
you will need to perform this backport manually.

[trop]

I have automatically backported this PR to "10-x-y", please check out #26394

[trop]

I have automatically backported this PR to "11-x-y", please check out #26395

[trop]

@zcbenz has manually backported this PR to "9-x-y", please check out #26506