Codegen of vkjson

The vkjson_generate.py script generates vkjson files from data in
vkjson_constants.py. While ideally vk.xml would serve as the source (a
future improvement), deriving vkjson_constants.py from vk.xml is a
separate task. To maintain concise CLs, this derivation will be
addressed in a separate CL. Adding symbols (features, properties,
extensions, limits) to vkjson is now straightforward. Simply define
their dependencies within vkjson_constants.py, and the script will
automatically update vkjson.h, vkjson.cc, and vkjson_instance.cc
accordingly.

Test: adb shell cmd gpu vkjson
Flag: NONE infeasible
Bug: b/401180969

Change-Id: I3652e80c465145e86cc4c25f79523a6dc2111d18