Add nesting limit for `JsonReader`

[Marcono1234]

Purpose

Add nesting limit for JsonReader

Description

For now don't expose this as additional GsonBuilder method assuming that the default nesting limit is high enough for most users. Otherwise users can first obtain a JsonReader from Gson.newJsonReader and then set a custom nesting limit.

The reasons why this pull request makes the nesting limit configurable at all are

• that some users might want to even further decrease the limit, for example if their call stack is already quite large before Gson is called
• and because JsonReader can be used directly in a way which does not involve recursion, so for these advanced use cases there might be no limit needed. It appears there are rare cases where users need to handle more deeply nested JSON data; here are examples from other programming languages: https://github.com/valyala/fastjson/issues/65, https://github.com/serde-rs/json/issues/162#issuecomment-713662554

Checklist

• [x] New code follows the Google Java Style Guide\ This is automatically checked by mvn verify, but can also be checked on its own using mvn spotless:check.\ Style violations can be fixed using mvn spotless:apply; this can be done in a separate commit to verify that it did not cause undesired changes.
• [x] If necessary, new public API validates arguments, for example rejects null
• [x] New public API has Javadoc
  • [x] Javadoc uses @since $next-version$
    ($next-version$ is a special placeholder which is automatically replaced during release)
• [x] If necessary, new unit tests have been added
  • [x] Assertions in unit tests use Truth, see existing tests
  • [x] No JUnit 3 features are used (such as extending class TestCase)
  • [ ] If this pull request fixes a bug, a new test was added for a situation which failed previously and is now fixed
• [x] mvn clean verify javadoc:jar passes without errors

[Marcono1234]

@eamonnmcmanus regarding https://github.com/google/gson/discussions/2632#discussioncomment-9481105: Is there some general problem with this concept of a nesting limit or should I change something?

[eamonnmcmanus]

@eamonnmcmanus regarding #2632 (reply in thread): Is there some general problem with this concept of a nesting limit or should I change something?

Last time I looked, this triggered a test failure in a Google-internal test. I think what I might do is patch Google's internal copy of the Gson source code to increase the threshold so that test passes. I think the limit of 255 is reasonable for the public version. I'm looking into this now.