[flang] Normalize logical values during type conversions.

Flang was missing value normalization for logical<->integer conversions
which is required by Flang specification. The shrinking logical<->logical
conversions were also incorrectly truncating the input.
This change performs value normalization for all logical<->integer
conversions and logical<->logical conversions between different kinds.

Note that value normalization is not strictly required for
logical(kind=k1)->logical(kind=k2) conversions when k1 < k2.

Differential Revision: https://reviews.llvm.org/D147019