This patch replaces the `SingleBlockImplicitTerminator<"TerminatorOp">`
trait of loop wrapper operations for the `SingleBlock` trait. This
enables a more robust implementation of the
`LoopWrapperInterface::isWrapper()` method, since it does no longer have
to deal with the potentially missing (implicit) terminator.
The `LoopWrapperInterface::isWrapper()` method is also extended to not
identify as wrappers those operations which have a loop wrapper
operation inside that is not taking a wrapper role. This is important
for cases where `omp.parallel` is nested, which can but is not required
to work as a loop wrapper.
Tests are updated to integrate these representation and validation
changes.
d6fb899034