SQL/JSON: Fix error-handling of some JsonBehavior expressions

To ensure that the errors of executing a JsonBehavior expression that
is coerced in the parser are caught instead of being thrown directly,
pass ErrorSaveContext to ExecInitExprRec() when initializing it.
Also, add a EEOP_JSONEXPR_COERCION_FINISH step to handle the errors
that are caught that way.

Discussion: https://postgr.es/m/CACJufxEo4sUjKCYtda0_qt9tazqqKPmF1cqhW9KBOUeJFqQd2g@mail.gmail.com
Backpatch-through: 17

src/backend/executor/execExprInterp.c

@@ -4558,6 +4558,12 @@ ExecEvalJsonCoercionFinish(ExprState *state, ExprEvalStep *op)
 		*op->resvalue = (Datum) 0;
 		*op->resnull = true;
 		jsestate->error.value = BoolGetDatum(true);
+
+		/*
+		 * Reset for next use such as for catching errors when coercing a
+		 * JsonBehavior expression.
+		 */
+		jsestate->escontext.error_occurred = false;
 	}
 }