If a schema contains a message named e.g. FooT and a message named Foo
while the Object API suffix is T, then two classes with colliding names
will be generated. This scenario will produce a C++ compiler error, but
it's confusing.
This patch moves the error to the compiler, allowing the user to more
readily act to correct the issue.
Co-authored-by: Michael Beardsworth <beardsworth@intrinsic.ai>