lib: fix `BroadcastChannel` initialization location
Refs https://github.com/electron/electron/issues/37417. Refs https://github.com/nodejs/node/pull/40532. Refs https://github.com/electron/electron/pull/37421.
Fixes a bug wherein BroadcastChannel
should have been initialized in lib/internal/bootstrap/browser.js
instead of lib/internal/bootstrap/node.js
. That inadvertently made it such that there was incorrect handling of the DOM vs Node.js implementations of BroadcastChannel
.