Move bouncefix.add('pinny__content') into pinny open to fix scroll jank on some sites

[tedtate]

Status: Opened for visibility Reviewers: @kpeatt @scalvert

Changes

• Move the initialization of bouncefix into pinny.open
• Removes bouncefix when pinny is closed

  Notes

• On some sites it seems like pinny can introduce some pretty bad scroll jank and the cause of the jank comes from bouncefix. This change fixes that issue.
• It would be nice if we could figure out in what situations the jank is introduced. Because it does not seem like bouncefix has this effect in all situations.

[kpeatt]

Haven't tested but the change makes sense to me.