BCodeOpt: NullnessPropagator takes module load for non-null

The load of a MODULE$ field won't be elided.
However, the non-nullness tracked for that value might lead later on
to control-flow simplification.
BCodeOpt: test constant folding including nullness propagation

A test is added to verify branches are removed when their outcome
can be determined at compile time based on constant-folding and
nullness propagation.

The test is the BCodeOpt counterpart to the jvm test introduced in
commit 69109c0ace5e3ac831c3b0a5635f25317d3b28bf