Unit tests for vkjson_gen_util (Part 3/3)

Reference:
Part 1/3 CL -
https://googleplex-android-review.git.corp.google.com/c/platform/frameworks/native/+/33070222

Part 2/3 CL -
https://googleplex-android-review.git.corp.google.com/c/platform/frameworks/native/+/33433767

Bug: b/409449379
Flag: NONE infeasible
Test: No impact to vkjson src files. All 68 test cases pass when executed locally
Change-Id: I929ff0cb9390061af4d52c55b25c0a7689840bb4