[CVL] Add support for YANG map-list

[ayelrod]

This change adds support for YANG map-list and map-leaf extensions. This support was removed in #110 and without it, tables defined using map-list and map-leaf do not work.

[DanielaMurin]

@ayelrod
Hi, I noticed in the #110 commit that map-list and map-leaf were also removed from several yang files (sonic-ext). Are they not needed?

[VladimirKuk]

Can you add a test for these cases ?

[faraazbrcm]

@ayelrod

May I know the use case why you need map-leaf and map-list?

Previously it was present to support dynamic fields. But I corrected the implementation in CVL, because it was not adhering to the SONiC YANG guidelines. As per guideline a INNER TABLE should have a single key leaf and single non-key leaf, if the yang adheres to this model schema, the CVL will automatically support dynamic fields for such TABLE.

Please refer PR134, this has an example for table with dynamic fields.

Therefore we dont need these extensions anymore.

[ayelrod]

Thanks @faraazbrcm. I will use the new schema for supporting dynamic fields.