vulkan/util: add an option to combine all dispatch table into one struct

This changes vk_dispatch_table_gen.py and adds a flag --all-in-one to it Well, now it generates the table every time.

When the flag is enabled, the script generates a vk_full_dispatch_table that is a combination of all the other dispatch tables. Zink uses this since it does not need to differentiate all the entrypoints separately.

@zmike @jekstrand