NFC: BridgeJS: Further simplify codegen and JSValue intrinsics

[krodak]

Overview

• Refactor ClosureCodegen to remove duplicate closure type construction by extracting swiftClosureType(for:) and reusing it in both helper and invoke thunk generation.
• Simplify closure invoke ABI return handling by directly using loweringReturnInfo().returnType and remove now-unused local state.
• Refactor ExportSwift by extracting shared helpers for static context base name, constructor thunk rendering, and method thunk rendering reused across class/struct export paths.
• Simplify class property export rendering by collapsing static vs instance context selection to a single call site.
• Simplify stack lifting for arrays of imported JS class wrappers from manual inline stack loops to [JSObject].bridgeJSLiftParameter().map { Wrapper(unsafelyWrapping: $0) }.
• Remove an unused parameter from optional lowering internals in StackCodegen.
• Deduplicate JSValue payload retain logic in BridgeJSIntrinsics via bridgeJSRetainPayloadIfNeeded(kind:payload1:) and reuse it in both lift and lower paths.
• Simplify JSValue.bridgeJSLiftReturn() to delegate to the existing no-arg bridgeJSLiftParameter() path.