Adds the missing TFLite NonMaxSuppressionV4 frontend handler. The
underlying relax.op.vision.non_max_suppression already covers V4's
behavior with soft_nms_sigma at the default 0.0 (hard-NMS path). The
handler bridges TFLite's tensor format to the Relax op, following the
same pattern as convert_nms_v5 (#19426) but without its soft-NMS
branching.
Tests cover conversion and IR structural assertions, run with
`pytest tests/python/relax/test_frontend_tflite.py -k nms_v4`. E2E
correctness runs on the nightly gate (CI_ENV_NIGHTLY).
Relates to #19412.
as4230
c1415d6e4d