Swift: reject uppercase acronyms in schema

This was causing hardly debuggable errors because names are transformed
to underscored lowercase names in the dbscheme and back to camelcase
for trap emission classes, which is not a noop in case uppercase
acronyms (like SIL or ABI) are in the name.

This makes the error be surfaced early with a helpful message.

swift/codegen/test/test_schema.py

@@ -669,5 +669,16 @@ def test_null_class_cannot_be_defined_multiple_times():
                 pass
 
 
+def test_uppercase_acronyms_are_rejected():
+    with pytest.raises(schema.Error):
+        @schema.load
+        class data:
+            class Root:
+                pass
+
+            class ROTFLNode(Root):
+                pass
+
+
 if __name__ == '__main__':
     sys.exit(pytest.main([__file__] + sys.argv[1:]))