Add parsing for attributes and attibutes on operations.  Add IR representation
for attributes on operations.  Split Operation out from OperationInst so it
can be shared with OperationStmt one day.

PiperOrigin-RevId: 203325366
diff --git a/test/IR/parser-errors.mlir b/test/IR/parser-errors.mlir
index 684c5a9..897da80 100644
--- a/test/IR/parser-errors.mlir
+++ b/test/IR/parser-errors.mlir
@@ -91,3 +91,6 @@
 mlfunc @non_statement() {
   asd   ; expected-error {{expected statement}}
 }
+
+; -----
+