fix: shutdown after message loop is ready

[zcbenz]

Description of Change

When app.quit() is called while the message loop is not fully started, do not shutdown until message loop is ready.

Quitting too early would break Chromium's shutdown code, and leave a few defunct processes behind.

Close #16632.

Checklist

• PR description included and stakeholders cc'd
• npm test passes
• tests are changed or added
• relevant documentation is 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: Fix defunct processes after quitting.

[jkleinsc]

Looks good to me. The failing CI was a release test that shouldn't have run for this PR - so this PR can be merged.

[release-clerk]

Release Notes Persisted

Fix defunct processes after quitting.

[jkleinsc]

/trop run backport-to 5-0-x

[trop]

The backport process for this PR has been manually initiated,
sending your 1's and 0's to "5-0-x" here we go! :D

[trop]

I have automatically backported this PR to "5-0-x", please check out #16672

[deepak1556]

@zcbenz should this be backported to 4-0-x as well, where the changes originated from f5eaa97#diff-735da1d7bca6fa4542f4eea75dc6595d

[zcbenz]

@deepak1556 4-0-x is working fine so I think we can leave it be. It is required in 5-0-x because CI is broken there.