Add app event: before-browser-window-created

[timfish]

It would be great to have a before-browser-window-created event that developers can use to create reusable modules that can globally intercept and modify BrowserWindow options before window creation.

It is already possible to do this for BrowserWindows passed through the webContents 'new-window' event but not for windows created from the BrowserWindow constructor.

This would be useful for reusable:

• Window managers
• Window state/position persisting
• Other things?

app.on(`before-browser-window-created`, (options: BrowserWindowConstructorOptions) => {
  // do something fancy with options?
});