[flang] Revert to returning default INTEGER for LEN() and offset-in-CHARACTER...

[flang] Revert to returning default INTEGER for LEN() and offset-in-CHARACTER intrinsics; further shape analysis of intrinsic results

Original-commit: flang-compiler/f18@561f5965b2309df3cd15d7e2a96d7e73f2f76e35
Reviewed-on: https://github.com/flang-compiler/f18/pull/782
Tree-same-pre-rewrite: false