Large json serialization/deserialization tests (dotnet/corefx#39668)
* Test large json serializaiton/deserialization
* Fixing test failure, applying feedback
* Add circular dependency test with large object
* Added test writing an object right at threshold level, removed unnecessary test cases
* Fixing typo
* Using VS generated POCO for test
* Addressing feedback
* Applying feedback
* Applying feedback
* Applying feedback
* Refactored the test Json schema
* Commenting failing case
* Applying feedback
* Applying feedback
* Enabling fixed tests
Commit migrated from https://github.com/dotnet/corefx/commit/
20334125a70444b5e8cf35f3f661911cd85a78b5