Re-enable the mapReduce jstests on the WASM JS engine. The C++ mapReduce support (`setupEmit`/`emit`/`Reduce`/`FinalizeReduce`) landed with the SERVER-127318 performance improvements, but four tests remained tagged `mozjs_wasm_unsupported`. This ports the outstanding test-side changes from the now-stale PR #55711.

*Key changes:*

• `internal_js_reduce.js`, `mr_bigobject.js`, `mr_bigobject_replace.js`, `constructors.js`: replace `mozjs_wasm_unsupported` with `tsan_incompatible` / `incompatible_aubsan` (TODO SERVER-128404), matching the tags already on `js_object_properties.js`
• `internal_js_reduce.js`: trigger error 31392 host-side with 2 × 9 MB values instead of a 20 MB working set
• `mr_bigobject.js`: reduce working set from 30 MB to 18 MB to avoid OOM on memory-constrained multi-node hosts; tag `incompatible_with_initial_sync`
• `mr_bigobject_replace.js`: drop shell asserts from the reduce/finalize function, which runs server-side where the shell assert library is unavailable
• `replica_sets_reconfig_jscore_passthrough.yml` (+ regenerated matrix suite): exclude `mr_bigobject.js` because background reconfigs interrupt slow WASM mapReduce on arm64 (TODO SERVER-128420)