Resurrect back-before-hydration tests from #95682
#95682 was reverted, which also removed its regression tests. Restore
them so the behaviors stay on record for a future fix.
On top of the revert, the two 'reconciles …' tests fail (the original
bug: a Back press between a reload and hydration leaves the URL bar
and the rendered content permanently out of sync). The 'other history
changes before hydration' tests describe behavior that predates
\#95682 and should pass.
