[Kernel] Add Default client implementations

[vkorukanti]

Context

This PR is part of #1783.

Description

Following client implementations for the default module are added:

 * `JsonHandler`
 * `ExpressionHandler`
 * `FileSystemClient`

and the supporting classes.

How was this patch tested?

UTs

[allisonport-db]

should we check for nullable field here too?

[vkorukanti]

its not needed here. We do a check before coming here. There are couple of places the check needs to be done when parsing the array element or parsing the map value element. Added a checks to throw exception of the null type is not expected.

[allisonport-db]

I thought this is different from rootNode.get(name) == null as it's a json literal null value?

[allisonport-db]

propagate the exception?

[vkorukanti]

Utils.closeCloseables already throws an unchecked exception.

Related to this: The iterator interface needs to have some kind of checked exception throwing, but we can't override the interface. Added this to the list. We may need to revisit this. Unchecked exceptions are not always good.

[allisonport-db]

Isn't the original exception e suppressed here though?

[allisonport-db]

+1 on the iterator interface

[vkorukanti]

No its not.

            if (exception == null) {
                    exception = new RuntimeException(ex);
                }
                else {
                    exception.addSuppressed(ex);
                }

We keep the first exception (wrap it in RuntimeException because of the no-checked exceptions). Subsequent exceptions are added to suprrssed. they are still available, but won't be printed.

[allisonport-db]

I mean whatever exception caused us to reach the catch block here at all. Not sure if I'm missing something obvious

[allisonport-db]

If we fail to open the file or something and stream = null we just continue on here no?

[vkorukanti]

Ok, got it. Added a silent close version of the API. I think this exception e is the main one we want to preserve.

[allisonport-db]

LGTM