fix: nativeImage.createThumbnailFromPath and shell.openExternal in renderer

[nornagon]

Description of Change

nativeImage.createThumbnailFromPath wasn't resolving when called in the
renderer. This started happening in #37701, I think Chromium stopped pumping
the Grand Central Dispatch queue in renderer processes. I haven't figured out
the exact change which caused the regression, but relying on Chromium's own
dispatch queues fixes the issue.

Fixes #41816.

Checklist

• PR description included and stakeholders cc'd
• npm test passes
• tests are 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: Fixed nativeImage.createThumbnailFromPath and shell.openExternal not resolving when called in the renderer process.

[gaodeng]

Could this PR be ported to version 27.x ？ Many of us are still unable to upgrade to 28.x due to this issue: electron-react-boilerplate/electron-react-boilerplate#3568 . Much appreciated!

[codebytere]

@nornagon it was https://chromium-review.googlesource.com/c/chromium/src/+/4369441 i believe!

[nornagon]

@gaodeng v27 is no longer supported unfortunately: https://www.electronjs.org/docs/latest/tutorial/electron-timelines

[nornagon]

Updated this PR to also fix shell.openExternal, which was failing for the same reason.

[release-clerk]

Release Notes Persisted

Fixed nativeImage.createThumbnailFromPath and shell.openExternal not resolving when called in the renderer process.

[trop]

I was unable to backport this PR to "28-x-y" cleanly;
you will need to perform this backport manually.

[trop]

I was unable to backport this PR to "29-x-y" cleanly;
you will need to perform this backport manually.

[trop]

I have automatically backported this PR to "31-x-y", please check out #41908

[trop]

I have automatically backported this PR to "30-x-y", please check out #41909