Add public current depth field to JSON reader.

[ahsonkhan]

Fixes #1744

The following snippet can now be re-written using public APIs:

azure-sdk-for-c/sdk/src/azure/iot/az_iot_hub_client_properties.c

Line 242 in 75afd98

if (jr->_internal.bit_stack._internal.current_depth == 0)

As follows:

if (jr->current_depth == 0)

Note when the depth is incremented:

0 {
1, 1	"foo": 123,
1, 1	"bar": {
2, 2		"baz": 1
1	}
0 }

cc @danewalton

[ahsonkhan]

@JeffreyRichter, do you think it makes more sense to expose this field from the az_json_token struct rather than from the az_json_reader? I have it from the reader because it is easier to access from the caller (the user doesn't have to fish it out from the nested token field), but the depth can be thought of as a property of a particular JSON token.

[RickWinter]

Can you share the customer code that uses this field. The usage patterns would probably highlight if it should be on the reader on the token.

[ahsonkhan]

I did above in the PR description.

[ahsonkhan]

The reason why I didn't want to add it to the token is, right now, the token can be created as a standalone type, and used outside of the reader (at least when looking at the public fields). Adding depth to it turns it into something that has to be a part of a larger JSON payload (and then we might not be able to use it in the future for other cases like in the writer).

Also, in .NET, I had added the depth on the reader directly (but we didn't have the nested token struct there) :)

The reason why I posed the question is because I feel that if we emphasize single responsibility, a case can easily be made to move the field to az_json_token.

[ahsonkhan]

All that said, this is still in beta and we can revisit it separately, if necessary.

[danewalton]

fwiw I'd prefer in the json reader rather than the token unless there's a good reason for it to be in the token.

[ahsonkhan]

Will close on it later, and decide if a change is needed or we are happy where we are:
#1808

[ahsonkhan]

@RickWinter or @antkmsft any other feedback or thoughts before I merge this?