YANGTOOLS-766: introduce JSONCodecFactorySupplier

YANGTOOLS-766: introduce JSONCodecFactorySupplier

We need two separate instances of JSONCodecFactory factory methods,
each with its own conformance, so that we can properly spin out
codecs compliant to RFC7951 and draft-lhotka-netmod-yang-json-02.

This patch provides a new API entrypoints for specifying these, without
actually providing distinct codecs. It also provides proper JsonParserStream
factory methods which take JSONCodecFactory instead of plain SchemaContext
(and thus assuming JSONCodecFactory implementation).

Change-Id: Ib2b402ed865903432645632e89c9b0e04851a05c
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>