Fix iOS long-press selection latching on forever

[MarcelKaeding]

Fixes the long-standing iPad/iPhone bug where the document editor gets stuck in a "select-and-highlight" mode: a permanent magnifier, every drag highlighting text by word, and the list slowly auto-scrolling until the magnifier hits the top of the screen. It only clears when something rebuilds the interactor — which is why the reported workaround (open Talk, dismiss it) "fixes" it.

Cause

_onLongPressDown starts a long-press selection and shows the magnifier, but it doesn't set _dragMode — only _onPanStart does. The only path that ends a long-press, _onLongPressEnd, is reachable exclusively through _onDragSelectionEnd, which requires that _dragMode.

So a long-press that never becomes a drag is never torn down. _longPressStrategy stays non-null, and since EagerPanGestureRecognizer.shouldAccept returns true whenever _isLongPressInProgress, the next unrelated pan anywhere in the document is claimed as a long-press drag-selection — magnifier up, auto-scroller running, no drag end to take either back down.

It's reachable whenever the pointer is taken away after the long-press timer fired: another recognizer wins the arena, or a widget's hit-test behaviour changes mid-gesture. Superlist hits it by moving focus between a list's title and its body, which flips every task component between opaque and translucent hit-testing.

Android has never had this — its _onTapUp and _onPanCancel both end an in-progress long-press. This mirrors that on iOS.

Changes

• End the long-press in _onPanCancel even when no drag started.
• End it in _onTapUp too, and skip that method's ordinary tap handling so the release doesn't toggle the just-revealed toolbar back off. _didEndLongPressDuringCurrentGesture coordinates the two, since both fire for the same pointer and _onPanCancel runs first.
• Keep showing the toolbar on release when the long-press produced a collapsed selection (e.g. an empty paragraph), which _onLongPressEnd alone doesn't do.
• Cancel _tapDownLongPressTimer in dispose(). It's armed on every tap-down and lives outside the gesture arena, so it can outlive the State and raise a magnifier on the ancestor-owned controls controller that no interactor is left to lower.
• Make _updateOverlayControlsAfterFinishingDragSelection null-safe on the selection, now that it also runs from the tap-up and pan-cancel paths.

Testing

Adds a regression test for the cancelled-press case — without the fix, the following drag raises the magnifier.

Full suite on this branch: 5564 passing, versus 5563 on the branch point, with an identical set of 11 pre-existing failures. No regressions.

Not yet verified on a physical iPad — worth walking the original reporter's steps on a device before closing their report.