Fix ko.unwrap for find/findLast/at(-1) results in LINQ JS translation (FirstOrDefault/LastOrDefault with predicate)

[Copilot]

Regression in v5: FirstOrDefault(pred), LastOrDefault(), and LastOrDefault(pred) JS translations generated a hard observable call expr() on the returned array item. When array items are plain mapped objects (e.g. control property arrays), calling the item as a function throws at runtime.

Root cause

firstOrDefaultPred, lastOrDefault, and lastOrDefaultPred translators in JavascriptTranslatableMethodCollection.cs annotated their result with VMPropertyInfoAnnotation without isObservable: false. This caused JsViewModelPropertyAdjuster to set ResultIsObservableAnnotation, which then caused KnockoutObservableHandlingVisitor to emit a hard expr() unwrap — correct only when items are guaranteed to be ko-observable functions, but not when they're plain objects.

Before:

// FirstOrDefault(f => f.KlicRazeni == "")
array().find((f) => ko.unwrap(f).KlicRazeni() == "")()  // item() — fails if item is plain object

After:

array().find((f) => ko.unwrap(f).KlicRazeni() == "")  // ko.unwrap — safe for both observables and plain objects

Changes

• firstOrDefaultPred (find): add isObservable: false + ResultMayBeObservableAnnotation → emits ko.unwrap(find(pred)) instead of find(pred)()
• lastOrDefault (at(-1)): same pattern → ko.unwrap(at(-1)) instead of at(-1)()
• lastOrDefaultPred (findLast): same pattern → ko.unwrap(findLast(pred)) instead of findLast(pred)()

ko.unwrap is already used for lambda parameters inside predicates (e.g. ko.unwrap(f) inside find), making this consistent. For actual ko-observables ko.unwrap(x) === x(), so the behavior is equivalent; for plain objects it returns the object itself rather than throwing.

Note: Where(pred).FirstOrDefault() (Variant B from the issue) goes through BuildIndexer which is not changed in this PR. That path requires a more targeted fix to avoid affecting Select-mapped arrays where items are already plain values.

• Fixes FirstOrDefault/Where().FirstOrDefault() with property-comparing predicate broken in JS translation (v5) — regression of #1870/#1871 #2105