Port closed default serializers of simple arrays

Opt-in default-encoder port of a fresh default JavaScriptSerializer local whose only bound reads are Serialize calls on arrays of strings, Booleans or built-in integers. Keep the local initialization position with an object marker, capture marker/array in order, then preserve receiver-null checks, null arrays, IEnumerable traversal, invariant integer tokens, Boolean tokens and default string escaping. Retain default output-size/error policy; do not turn byte arrays into base64. Leave configuration, reassignment/escapes, other calls/elements/overloads, named calls, comments, lambda/query contexts, partial/generic owners, aliases/scoped imports and snapshots unchanged. Custom encoders/ampersand settings, localized error text, allocation identity and debugger/local-name contracts are not emulated. Separate from version upgrades; Core 3.0 or later.