fix: respect minimizable/closable for customButtonsOnHover

[codebytere]

Description of Change

Fixes #18364.

This PR ameliorates an issue whereby minimizable and closable weren't respected in customButtonsOnHover mode. maximizable isn't addressable here, since it's been blanket disabled in newer versions of macOS owing to an issue with the NSWindowStyleMaskFullSizeContentView style mask. That will, however, be addressed in the relevant backport pull request.

This can be backported to 6 as-is but will need to be manually backported to 5 & 4 to account for the maximizable consideration.

cc @pronebird @MarshallOfSound @nornagon @miniak

Checklist

• PR description included and stakeholders cc'd
• npm test passes
• PR title follows semantic commit guidelines
• PR release notes describe the change in a way relevant to app developers, and are capitalized, punctuated, and past tense.

Release Notes

Notes: Fixed an issue whereby minimizable and closable weren't respected in customButtonsOnHover mode.

[nornagon]

This code is a mystery to me but it looks relatively fine.

[release-clerk]

Release Notes Persisted

Fixed an issue whereby minimizable and closable weren't respected in customButtonsOnHover mode.

[trop]

I was unable to backport this PR to "6-0-x" cleanly;
you will need to perform this backport manually.

[trop]

A maintainer has manually backported this PR to "6-0-x", please check out #18478