Add model for test case

src/test/resources/streamtests/multipleAssignmentsBase/test/MultipleAssignments.emam

+package test;
+
+component MultipleAssignments{
+       ports
+            in Q a,
+            out Q c;
+
+        implementation Math{
+            Q b = 42 + a;
+            c = 1 + b;
+
+            b = 43;
+            c = 1 + b;
+        }
+}
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src/test/resources/streamtests/multipleAssignmentsBase/test/MultipleAssignmentsTest.stream

+package test;
+
+stream MultipleAssignmentsTest for MultipleAssignments{
+    a: 10;
+    c: 44;
+}
\ No newline at end of file