Updated libyang library to support more than 255 typedef statements

[ygorelik]

Updated libyang library.
Adjusted YDK core to work with new libyang library.
Added test to check how new libyang library handles more than 255 typedef statements (450 in the test).

[codecov]

Codecov Report

Merging #678 into master will increase coverage by 0.03%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #678      +/-   ##
==========================================
+ Coverage   74.14%   74.17%   +0.03%     
==========================================
  Files         104      104              
  Lines       10444    10453       +9     
  Branches     1467     1467              
==========================================
+ Hits         7744     7754      +10     
  Misses       2397     2397              
+ Partials      303      302       -1

Impacted Files	Coverage Δ
sdk/python/core/tests/test_sanity_codec.py	94.65% <100%> (+0.27%)	⬆️
sdk/python/core/tests/test_on_demand.py	98.14% <100%> (ø)	⬆️
ydkgen/printer/meta_data_util.py	79.37% <0%> (-0.45%)	⬇️
ydkgen/api_model.py	78.07% <0%> (+0.33%)	⬆️
sdk/python/core/ydk/types/py_types.py	84.67% <0%> (+0.4%)	⬆️

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[ghost]

Looks great! Thanks @ygorelik