feat: add <webview>.sendToFrame() / frameId to 'ipc-message' event

[miniak]

Description of Change

This allows replying to an IPC sent by a frame (when nodeIntegrationInSubFrames is enabled) inside of the <webview>:

webview.addEventListener('ipc-message', event => {
  webview.sendToFrame(event.frameId, event.channel, ...event.args);
});

Fixes #30207.

Checklist

• PR description included and stakeholders cc'd
• npm test passes
• tests are changed or added
• relevant documentation is 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: Added <webview>.sendToFrame() / frameId to 'ipc-message' event.

[ryankashi]

webview.sendToFrame with passing in the frameId looks good to me!

[zcbenz]

API looks good to me.

[samuelmaddock]

API LGTM

[codebytere]

@miniak could you please rebase this? In addition - needs one more button-click API LGTM (@nornagon maybe?)

[miniak]

@codebytere conflicts resolved

[nornagon]

API LGTM. button click is a bit pointless b/c it gets reset by any rebase or other change.

[miniak]

@codebytere can we merge this now?

[release-clerk]

Release Notes Persisted

Added <webview>.sendToFrame() / frameId to 'ipc-message' event.

[trop]

I was unable to backport this PR to "15-x-y" cleanly;
you will need to perform this backport manually.

[trop]

@miniak has manually backported this PR to "15-x-y", please check out #30704