I extracted this utility function from #3207 to make TypeScript isArray() checks safer by preserving the element type, not assuming they're any.

TypeScript's built-in types for Array.isArray() incorrectly uses any[]. It should use unknown[]. The consequence of using Array.isArray() is that even if you've narrowed a value to a more specific type, TS will treat it as any after the check, which effectively disables type-checking.

In this PR, as a demonstration, I only converted a few call sites until I hit one that had a cascading effect that triggered a type error near the call site. In massageFormats(), the new Vector3(a[0], a[1], a[2]) became an error since TS could no longer assume that a[i] was any. I addressed it by making the massageFormats() function parameter type more accurate, and this cascaded to the caller of that, where I added an early return.

Relevant issues:

• Array.isArray type narrows to any[] for ReadonlyArray<T> microsoft/TypeScript#17002
• Array.isArray refinement loses the array's type microsoft/TypeScript#33700