Add e2e tests that prove we can edit an old version of a component

Good call.

Especially important now that we've discovered (and fixed) 🐛 Data loss: `ComponentTreeItem::setValue()` and `::onChange()` may inappropriately upgrade `component_version` to the latest version Active (and kinda also 📌 Disallow component trees with `component_version: active` Active ). This would be the finishing touch to boost our confidence 🤓

I went looking for any existing tests that enable xb_test_storage_prop_shape_alter which would be the obvious way to test this and found component-transforms.cy.js which looks to do exactly what we were looking for here.

That was added in 🐛 Component transforms need to be per sourceType, not per component prop Active which was early May, but this issue was opened in June - so that leads me to believe it might not be enough on its own.

I will recreate the steps in that test and see if it is already providing the coverage we need and expand it as needed.

Expanded the existing test to assert that the input in the old component version passes validation.
Because our validation is tied to the json schema and that _doesn't_ change I think we're in good shape here

That was fast!

I'd have liked to see a more comprehensive end-to-end test, but I see now that the issue summary was quite specific about this: so 👍

It is very nice to see such a nice little expansion of an existing test though, so merging this; more expansive test coverage will be necessary in 📌 [later phase] When the field type for a PropShape changes, the Content Creator must be able to upgrade Postponed anyway :)