[lavrton]

What does this PR do and why?

Two changes to applySnapshot on arrays of identified children.

1. A moved child keeps its node. Since Optimize applySnapshot for mostly unchanged snapshots #2285 an unchanged-length snapshot assigns each changed index in place, which reconciles against the one node at that index. When a child moved, every index between its old and new position gets a new node. Now, when a changed entry carries the identifier of another current child, the array uses replace, whose reconciliation finds the node by identifier and moves it. In Polotno, undoing one page reorder in a 100-page document recreated 71 pages; now none.

2. A snapshot is validated once. areSame validated a candidate (type.is) before comparing identifiers, so during reconciliation's look-ahead an inserted snapshot was validated once per following child. The identifier check now comes first for plain types; a snapshotProcessor keeps the old order, since its preProcessor may throw on a snapshot of another union member (union.test.ts).

Steps to validate locally

• bun test __tests__/core/array-apply-snapshot-moves.test.ts — all three tests fail on master.
• NODE_ENV=development bun test and MST_TESTING=1 NODE_ENV=production bun test are green.