Unit tests for vkjson.h generation

Will be adding the unit tests for the generation of vkjson.cc and vkjson_instance.cc in separate CLs

Reference:
To be merged after https://googleplex-android-review.git.corp.google.com/c/platform/frameworks/native/+/33433767

Bug: b/409449476
Flag: NONE infeasible
Test: No changes to the vkjson files after regeneration. All unit test cases (53 + 1) pass when executed locally
Change-Id: If740d55094f8e40727f3bb490682870b3dfd461f