The verifier's type checker is required to check that a type returned
from a method (an areturn instruction) is assignable to the method's
declared return type. When the return type is an interface, the JLS
states that it should be treated as java.lang.Object. This means that
no analysis of the type being returned is required and verification
passes. When the return type is a class, the type being returned must
be analyzed to ensure that it is compatible. This analysis causes the
return type to be loaded during verification.

Prior to this commit, BasicBatchConfigurer's
createAppropriateTransactionManager method had a return type of
AbstractPlatformTransactionManager and a branch that could return
a JpaTransactionManager. This caused the verifier to attempt to load
JpaTransactionManager so that it could check that it was assignable
to AbstractPlatformTransactionManager. This would fail when
spring-orm is not on the classpath as JpaTransactionManager could not
be loaded.

This commit updates BasicBatchConfigurer to change the return type
of createAppropriateTransactionManager so that it returns a
PlatformTransactionManager which is an interface. As described above,
this relaxes the verification of any areturn instructions in the
method and, in this particular case stops the verifier from trying to
load JpaTransactionManager.

Closes gh-8181