While fixing Bug 1773368, I accidentally introduced some uses of js::Handle in the code instead of the canonical JS::Handle. Since there are a number of pre-existing related issues, I am creating this new bug to tackle them together. The NamespaceImports.h header is used within Spidermonkey internals to avoid JS:: prefixes while working in js:: namespace. When writing signatures for non-namespaced types (like JSFunction), we need to typically qualify common types and we should prefer the canonical version instead of the namespace import.

(This is just minor house-keeping)