Fixing pyang "uses" expansion handling

[BrianSipos]

There was inconsistent use of pyang Statement.search_one() and Statement.search() which was producing duplicate subordinate statements in cases where a grouping was used containing object-subordinate keywords like amm:parameter or amm:operand. This update makes explicit use use the search "children" parameter to determine whether to look in direct children only (the default) or include uses-copied substatements.

This also fixes an issue that the ARI text encoder wasn't properly handling dict parameter type.

[justinethier]

@BrianSipos In addition to the review comments it's a bit unclear exactly why these changes were made. It might help to add more information to the PR. Also, do we need to add any additional tests for these changes?

[justinethier]

One minor issue but otherwise is good to go.