Refactor Converter type dispatch to remove chained instanceof tests

[vharseko]

Resolves both java/chained-type-tests CodeQL alerts in Converter (script/javascript). No behaviour changes; the module's 26 tests pass.

Changes

• wrap(Parameter, Request, Scriptable) — replace the instanceof chain over the Request subtypes with Request.accept(RequestVisitor). This reuses the existing json-resource visitor API, drops the repeated setBuiltinProtoAndParent call, and lets the compiler enforce that every Request subtype is handled. The original "we shouldn't get here" fallback is preserved via a null check.
• wrap(Parameter, Object, Scriptable, boolean) — replace the instanceof chain over unrelated types (Map, List, Function, JsonValue, JsonPointer, Request, Context) with an ordered Class -> strategy registry (LinkedHashMap), iterated in the same precedence as the previous if/else if chain. null handling and the Context.javaToJS(...) fallback are unchanged.

Notes

These types share no common hierarchy, so the second method is table-driven dispatch rather than true polymorphism — it removes the flagged instanceof chain while preserving the exact evaluation order and behaviour.

Verification

mvn -pl script/javascript -am test — RhinoScriptTest: 26 run, 0 failures, 0 errors.