Electron 7: wrong type for preloadURL vs preload

[bpasero]

The documentation of preload reads: This option will appear as preloadURL (not preload) in the webPreferences specified to the will-attach-webview event.

However the type is not present anywhere in electron.d.ts

//cc @MarshallOfSound

[nornagon]

This is a bit awkward because even though it's technically allowable to specify a file:// URL to WebPreferences anywhere via preloadURL, it's a bit useless to do so, since preload is right there and loads a path. #33228 to solve this a different way.