改进Calculator.conversion，兼容乘法符号省略写法

hutool-json/src/test/java/cn/hutool/json/Issue2953Test.java

@@ -0,0 +1,13 @@
+package cn.hutool.json;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class Issue2953Test {
+	@Test
+	public void parseObjWithBigNumberTest() {
+		final String a = "{\"a\": 114793903847679990000000000000000000000}";
+		final JSONObject jsonObject = JSONUtil.parseObj(a, JSONConfig.create());
+		Assert.assertEquals("{\"a\":\"114793903847679990000000000000000000000\"}", jsonObject.toString());
+	}
+}