fix: Correct modal focus behavior on macOS

[erickzhao]

Description of Change

Fixes #18502

This PR changes the focus and blur events that we emit in Electron to listen to changes in key window rather than main window. It swaps out windowDidBecomeMain and windowDidResignMain for windowDidBecomeKey and windowDidResignKey, respectively.

It seems to work as intended now. Also added a new test to test this exact situation. Please let me know if there's a less convoluted way to test this specific case, since it seems like I'm listening to a very specific series of events. Test seems to be working locally on my end, and fails on a downloaded CI build from master. ✅

Context

In our macOS code, the NativeWindowMac::Show() function in native_window_mac.mm calls this beginSheet function, which specifies that:

If the window has no presented sheets, this method displays the specified sheet, makes it key, and returns control to the caller. While the sheet remains visible, most events targeted at the receiver are prohibited.

For additional context, see Apple developer documentation on key and main windows here.

Fiddle: https://gist.github.com/c9c19684f6e0d23c102161fb3e86500b

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cc @codebytere @deermichel

Checklist

• PR description included and stakeholders cc'd
• npm test passes
• tests are changed or added
• 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 bug on macOS where the main window could be targeted for a focus event when it was disabled behind a modal.

[jkleinsc]

Nice work @erickzhao! Overall looks good to me - I would just make your new test a little more robust by verifying the main window can regain focus once the modal is closed.

[erickzhao]

@jkleinsc Seems like calling child.isDestroyed() and not relying on focus and closed emission ordering helped make the spec pass on Linux and Windows!

[release-clerk]

Release Notes Persisted

Fixed bug on macOS where the main window could be targeted for a focus event when it was disabled behind a modal.

[trop]

I have automatically backported this PR to "4-2-x", please check out #19061

[trop]

I have automatically backported this PR to "6-0-x", please check out #19062

[trop]

I have automatically backported this PR to "5-0-x", please check out #19063