[Feature Request]: Enable preloads in iframes without node integration

[rhysbrettbowen]

Preflight Checklist

• I have read the Contributing Guidelines for this project.
• I agree to follow the Code of Conduct that this project adheres to.
• I have searched the issue tracker for a feature request that matches the one I want to file, without success.

Problem Description

#16425 allows preloads for iframes, but only if nodeIntegrationInSubFrames is set to true. We would like to keep node integration off but allow us to run preloads in iframes.

Proposed Solution

create a new flag preloadInSubFrames to allow running just the preload without node integration

Alternatives Considered

use https://www.electronjs.org/docs/latest/api/web-frame-main to get a handle on web contents and inject through javascript. However does not have nice things like context isolation and exposeInMainWorld

Additional Information

No response