Keep ViewPosition consistent when a Document is edited from different Views, and on buffer switching

[intarga]

Supersedes #7568, fixes #7355.

Since view offsets can no longer be initialised in View::new(), I moved them next to selection initialisation in doc.ensure_view_init(view_id). I was a little concerned about all those unwraps on doc.view_data(view_id) (those functions are infallible and don't have a mutable reference to doc, so there's no way to ensure view_data is initialised in there), but in theory it should be panic-safe, as long as doc.ensure_view_init(view_id) is called for every new view, which it is. It was missing from some test cases, since they didn't seem to need selections, but it's added even to those now.

[intarga]

Can we get a retry on this test failure? It looks unrelated to my changes, and I can't reproduce it.

Ran the same commit through CI on my fork and got a pass https://github.com/intarga/helix/actions/runs/8790787504?pr=1

[archseer]

Something must have changed on the Github Actions runner, I'm seeing the same failure in other PRs.

[the-mikedavis]

Looks like macos runners switched from x86 to arm. Clearing the tree-stter-grammars cache for macos seems to have fixed it

[pascalkuthe]

this lgtm now and was a smaller change than I expected. I will test this out locally a bit