Adding tests for string.Equals constant short-circuit

Author: JohnDumbell

jbmc/regression/jbmc-strings/StartsWithConstantEvalution/RefineStrings.class

@@ -0,0 +1,12 @@
+package string_refinement;
+
+public class RefineStrings {
+    public void constantComparison() {
+        String helloWorld = "Hello world";
+        assert helloWorld.equals(helloWorld());
+    }
+
+    public String helloWorld() {
+        return "Hello world";
+    }
+}

jbmc/regression/jbmc-strings/StartsWithConstantEvalution/RefineStrings.java

@@ -0,0 +1,8 @@
+CORE
+RefineStrings.class
+--function string_refinement.RefineStrings.constantComparison --show-vcc --cp `../../../../scripts/format_classpath.sh . ../../../lib/java-models-library/target/core-models.jar`
+^Generated [0-9]+ VCC\(s\), 0 remaining after simplification$
+--
+.*cprover_string_startswith_func*.
+--
+All instances of cprover_string_startswith_func can be calculated as false or true, so there should be no instances of this call.