Expect `Expand All` or `Reexpand All` option

After selecting Collapse All for PRs or Issues, I'd then expect an option to either:

• Expand All
• Reexpand [issues or PRs] (perhaps preferable if we can remember what a user previously had open, and it'd reduce potential perf issues of trying to expand many links)

Or, I'd at least expect the Collapse All button to become unclickable if everything is already collapsed.