fix(browser): Reduce number of visibilitystate and pagehide listeners #18584

Previously, we called onHidden in our slightly modified version of the vendored in whenIdleOrHidden API from web-vitals. This caused 2 additional event listeners to be registered with each whenIdleOrHidden invocation, which also didn't get cleaned up properly.

To fix this, and prevent similar situations, this PR:

• inlines the pagehide event listener registration in whenIdleOrHidden so that we can remove the onHidden call
• adds once: true to the listener registration so that the callback is only invoked once
• deprecates onHidden because IMHO we should remove it in v11 and replace the one remaining use of it with a direct visibilityChange subscription.